Thank you,
Let's see...
1 - I'm no specialist in leather (I have an interior detailer that I've trained working with me while I'm detailing exterior so I've lost some interior ability on the long run), although I think Nick's thread suggestion would work on vinyl coated. You may ask him I believe he'll answer you promptly.
I've used cleaners and conditioners on Honda leather seats (from old to newer (2014) ones), I know what you are talking about... customers always appreciate how clean and soft their leather comes out, so I don't think of a waste here.
Try to use the least amount of product needed to get the job done. Also, I've already used APC for leather cleaning but I think leather dedicated cleaner is way more gentle on it, so I prefer dedicated cleaner. Just be assured to not use low quality products.
After cleaning, it's interesting to condition because leather may feel 'dry' after the process. In my opinion, just cleaning and letting leather feeling dry is a step away from dryness and tear / cracking.
I recommend you to let conditioning work for some minutes, then blot it 'dry' with a folded MF towel. It'll be soft enough using less product and blotting dry, avoiding (at least surface) dryness.
I cannot give you 100% precision on my answer, but if the above is terribly wrong, I'm sure some customer would let me know since they like what I do and keep returning often. I also do not see any harm caused by cleaner and conditioners, and I use them often.
For protection, I think there are few things like PBL leather coating, but some other companies offer similar coatings.
Also, many conditioners already comes with UV protection, so that may protect from sun, but for more protection you'll need to look further...
I believe it's worth looking at carpro product, but I haven't used it yet:
CarPro Cquartz Fabric & Leather Coating
Chemical guys serum looks interesting as well:
Chemical Guys Leather Serum, leather coating
Leather Master
Leather Master Leather Barrier, leather protectant
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Why do I use soap with nanoskin? Who said that? lol
Kidding apart, soap for nanoskin came with trial and 'error'. When I first got a clay on my hands (Perfect-it, from 3M), I've read on the label (something like that):
'use water + some drops of neutral soap as lube'.
I went through this route. Water, neutral soap, and although worked, I was not happy enough with this method. Searching the web I've found that quick detailing spray would work better, even some ONR, etc.
As soon as I could, I've got some detailer (meg's #34, quick detailer, etc) and found that for claying, they worked way better than the soap directions at 3M clay label. It's also easier and cleaner to wipe off quick detailer than soap when claying a dry car.
I was happy using detailing spray until nanoskin showed up. Ordered nanoskin, and this time I've started the opposite way, I mean, using detailing spray I was adapted to.
Again, although worked, I was not entirely happy with the method. That I could see with increased surface marring (but that was very easy to remove with fine polishing).
I've tried many combinations, until finding which would work best for me.
Just to advance, if I am about to clay an already washed and DRIED car, I'll lean towards detailing spray because that's easier than 'washing the car again'. It still works!
How I generally clay just after washing, I've played with plain water (works but not optimal), then with soap. In my opinion, the soap method for nanoskin works way better.
What is good to have in mind is that 'conventional clay' is tacky, and works 'adhering' the above surface contaminants, then you need to fold it often to expose a clean site. A detailing spray 'combines' with clay tackiness and method of use.
Nanoskin works differently, it's somewhat tacky, but works just like you are 'shaving' contaminants. Soap foam and lubrication 'combines' with nanoskin methods of use. I tend to rinse area often, and rinse my mitt often as well.
I've already tried to add some detailing spray to clay soap but that haven't improved from using only soap.
That said, I've also played with many kind of soaps... Ironically, I've found that Wash and Wax shampoo works wonders with nanoskin, since they look like a 'mix' of detailing spray (many are based on wax) and the foamy of soap. This added to the slickness of wax and soap, which for me is a win/win scenario.
Just like 'shaving', you have to 'GLIDE' it over surface. Use straight movements, not circular. Try to distribute the force EVEN over nanoskin, not making pressure with the tip of your fingers, in example (that's for claying also). To distribute pressure even, I like to put my hand OVER nanoskin instead of inside of it (I use the mitts).
Take a look (some pictures of different cars and soaps):
Combination that works great for me as nanoskin lube:
'Pre-Soak' my claying devices:
Foam the section to be clayed:
Use hand over to distribute force evenly:
Example of straight line movement I'm talking about (you may go back and forth the same region until feeling smooth):
This is how the surface may look after my process (clean and reflexive):
Taking a closer look, we see that I just removed above surface contaminants (picture above), while not leaving any marring on surface. Defects (horrendous swirls) in this case were still there, and was solved with polishing afterwards.
This picture is from the same car of last pictures when it arrived, still dirty, already swirled:
You can notice that claying alone improved the look of the car to a very reflective shine.
I always try to not add additional damage to what's already on car. I'm preparing the surface to have an EASIER time polishing, not harder.
I tell this because many may think 'if I'll polish anyway', I can instill swirls and scratches freely for later removal. Don't do this. Generally cars we detail already have enough damage. Use the same care (like 2 buckets, grit guards, clean towels and mitts, etc).
It's tempting to use pressure and scrub the nanoskin, although it will work anyway, I've seen more harm than good doing this.
Scrubbing with pressure may leave you with more marring than needed, also may scratch surface. You should use just ENOUGH pressure to maintain device plain to glide over surface. I've found that the more marring I leave, more work polishing afterwards and I don't want that happening.
Also, be even more gentle on places you'll not be able to polish adequately, since if you leave any marring there, it'll stay there. To solve it, polish trick areas you've clayed by hand.
Gliding will leave a slight marring (if any), that will go away easy with any pass of a polisher.
So, in conclusion, I've found that nanoskin with soap (IF claying just after washing, car still wet) works best for me. Not that it'll not work with other lubes (even with plain water), but I tend to stick with what works better in my situation.
If I'll not polish the car afterwards (or use an AIO), I tend to use nanoskin even lighter (just have to do more passes), and use a slick soap but not wash and wax.
If I'm going to polish and / or use a paint cleansing polish, there no problem with wash and wax, and that's what I generally use.
Hope that helps,
Please, let me know if you need additional info.
Kind Regards.