While OPC is by far the best APC/degreaser I own and it can remove browning from tires at 3:1 that super degreaser couldn't remove when used undiluted. That said, it certainly isn't what I would consider when trying to supplement D108 or D101 simply because of Power Clean's price point in the states. It's great to have on hand because it works better than any other cleaner undiluted or even diluted at 3:1. But at 10:1 it's cleaning ability drops off quite a bit where D108 Super Degreaser and D101 APC are still very effective at these higher dilution ratios which makes them a better value. If you decide to buy OPC, I think you could get away with 3:1 for exterior uses and 7:1 for interior.
If you have access to Mckee's 37 High Intensity APC+ I'd say it's a great supplement for D101 & D108. At 10:1 it's safe and very similar to Megs APC in terms of cleaning ability at this dilution. At 4:1 it's better than Meg's APC for exterior cleaning but I do think D108 is still a bit better at the 4:1 dilution ratio than mckee's so I'm not sure you could use it in place of both products for this reason.
Simple answer....
1. Optimum Power Clean overall is safest AND has the best cleaning power, so if you have access to it for less than the Meg's Products then that's a steal. Only other downside is poor cleaning ability at higher dilution ratios.
2. Mckee's 37 APC+ is probably the most comparable to D101 & D108 in it's foaming and cleaning ability at higher dilutions and has a pleasant scent.
3. Have not tried Chemical Guys All Clean+ but the dilutions are better than any of these products and it's suppose to be safe and effective for interior and exterior cleaning/degreasing
Too bad you don't have access to 3D products, they are simple and effective much like products in the meguiars detailer line