Welcome! What an honor to have my (nick)name cited being responsible for such step up in your detailing career.
To start, the 4 3/8 plate can be used with 5" pads (it's gorgeous with LC 5.5 pads), however the Hybrid pads has a 4" velcro face, and 5" polishing foam face.
That's the reason they won't be good with 4 3/8 plate, and are perfect for 4" interchangeable plate system.
About the Flex:
Someone who knows a thing or two about Flex polishers, once told me this:
I'd like to forward his words to you, since they are so spot on.
It arrived to me just after starting a work, so I had the pleasure to start using it right away.
Proudly holding it after the first tests
Imagine, this is what was left, at the end of the day, from the 'Unboxing' Thread I've promised doing when the Flex was to arrive. I was so excited!
This was the first work I did with it (on the day it arrived):
Not the best picture, but it can illustrate what happened that day.
I was also very thankful to Mike Phillips and Smack, both were crucial for my choice.
From that day on, I was able to improve the use on this tool, and I must admit I'm still learning more - the more I use, the more comfortable and natural I feel with it.
It's very comfortable to use, and it's mechanism of action will lead you to consistent results, all the time.
I'm adapted touching the paint with my hand while working to check if my process is generating a lot of heat. I don't go crazy about this, but I prefer being safe than sorry. 90% of time, the low amount heat generated is not an issue, indeed. Do this often just to check until you're comfortable.
This is specially more important in concavities, since the pad won't stop spinning, making the Flex as good to polish all shape of panels, but you have to pay attention to your technique.
Can't wait to hear about your first uses on it.
Even it being easy to use at first, don't be fooled by the short learning curve. It's sure you'll get great results and will not have an issue with it from the start, but the more you use it, the better (and BETTER) will be your outcome.
It has ample potential for pushing you to the limit. Go for it!
Thanks, again.
Kind Regards.