Huh?

I'm sorry Ken but all the above is exactly the opposite. For duration or speed flying the airfoil WILL work best with a proper shape and the trailing edge is part of that shape. Tests have shown that there is significant drag from having the trailing edges even 1% of the chord thick when applied to cases where efficiency counts like is sailplanes and speed models. And as for causing a stalling problem I've seen nothing to support that. A truncated airfoil will still stall at pretty much the same point as a sharp edge one. Selig did some wind tunnel work on this and the results showed a small degradation in lift and gains in drag with truncated trailing edges at all lift coefficients including near the stall.

I've never seen anything to show that a deflected surface will work better with a blunt TE than a sharp one. If there is something on this I'd love to see it. Other than the rounded to blunt comparison there's nothing out there to my knowledge.

The reason most sport models or trainers use flat surfaces with blunt edges is for simplicity of building and strength against twisting. The extra strength helps prevent flutter while at the same time the extra mass encourages it. But for the most part the extra thickness prevents it in most cases. Fun fly models in particular pretty much need the thick and blunt surfaces to provide the wood required to support the structure. But fly these a little too fast and they flutter like the dickens.

Beyond that the other two answers hit all the high points spot on. For gliders the 1/64 ply is quite popular but equally so is using basswood or spruce for the last 3/32 to 1/8 of thickness so it can be shaped down to a fine edge.

Oh, and FH, if you use the ply in short one foot segments with the face grains running chordwise instead of span wise you can sand it down even further to a true knife edge. I have not done it that way yet, only as you described on two models, but I've read about a few souls that do it that way. Then when covering you can run the material about 1/64 to 1/32 past the edge to glue the top cover to the bottom for a nice sharp two covering thickness edge. Now THAT is pretty sharp.... and probably a bit too over the top since I just thought of it...

But all this is more for fast models, electrics or sailplanes. The differences are not that large and when there's a big oily noisemaker up front it doesn't really matter. In fact there are very few models that are as INefficient as modern funfly models. But light weight, lots of wing area and much better than 1:1 power to weight ratios mask all that. In truth the drag of these models is actually designed in to help limit the speed gains during burst of high throttle or when diving.