Normally a large object in front of the lens projects a small image behind it, onto the sensor. When you flip the lens, a "small" object "behind" the lens projects a "large" image in "front" onto the sensor. Basically, the magnification ratio is flipped. (I haven't done the math, so it may not be exactly like that.)

• The max extension I can get with tubes is about 40-45mm. With a 28/2.8 lens and extension tubes, I get about 1.4:1.

  

• With a lens reversal adapter and 15mm extension, I get about 2:1.

  

I don't do any real macro photography, and have no idea which is "better". Except for the ease of obtaining a greater magnification ratio, they seem about even.

• The exposure difference wasn't significant. (ISO 1000 vs ISO 800).

• The lines in the reversed-lens image look a little straighter. But how much does this matter when not photographing rulers?

• I have no way to test sharpness at this level. If you have good lenses, they'll probably be sharp enough. I shot my test images handheld and wide open. They'd be much better stopped down on a rail.

• As you've noted, image stacking and averaging improves image quality. It may not be possible to do significantly better even if image quality of the source images is improved.

It seems as if it would come down to:

• Convenience factors you've already mentioned, like how easy it is to attach bayonet mounts vs screw adapters onto filter threads and whether you can control the aperture.

• Whether you can get the magnification you need with the equipment you have.

Since you get results you like, there may be no need to change. But it might be worthwhile for you to try. The adapters are cheap enough to buy several to leave attached to the lenses you like to use, so there wouldn't be any more "effort" than it takes to swap lenses normally. You could get a lens reversal adapter that fits your current extension tubes to increase the flexibility of your current setup.