I'm working on a Tamiya P-38H-5 at the moment. I've just gotten to the point of starting to apply Quinta's parts; just finished placing the parts for the main switch panel that goes under the main instrument panel. I also have a Tamiya P-38F/G, which I want to convert to a P-38H-1, which requires only a few small changes. When I got the kits, there was no Quinta set for the H, so I am using the Quinta sets for the F & G, with a photoetched instrument panel. Quinta now does have a set for the H, but the only difference I can see is the instrument panel. There will be a mix of the 3D parts with a few spare PE details.
Anyway the small toggle switches are impressive. I would not have wanted to paint all of those; not sure I could have done so neatly, these days. Any instruments on various panels are well-detailed, beneath clear "glass" faces.
Just to add to what was said by others, in spite of the name, they are not really "decals" as we know of them. The first order of business is to remove the raised detail on the plastic part. If possible, the plastic should be sanded so as to account for the thickness of the 3D item. On the switch panel, I painted the plastic a semi-gloss black. Although on a sheet, they are actually a vinyl material, built up on a paper backing sheet mainly for convenience. After a short soak, the parts come off the paper easily, and should be set on a paper towel to dry. The back of the parts is white, and they are very flexible. I used a white craft glue to affix the parts. The ones I've added so far do fit the part very well, and the small details are impressive. I'm looking forward to adding the rest of the cockpit details this week.
I have purchased one set of WWI German 2-seater belts from Kits-World, but haven't had a chance to try them yet.
Pete