TargetTalk

A couple of points about lenses and mountings:

The internally mounted lens is OK except that it must be disassembled for cleaning and indexing for astigmatism would appear to be a little tricky.

The astigmatic correction can vary slightly over time. With glasses you can quite easily rotate the lens slightly to achieve a better picture, this again is more difficult with the internally mounted lens.

If you are correcting for myopia it would be advantageous to have the lens closer to the eye than further away.

Eyesight can vary quite markedly with age. The older you are the more important it is that you have an eye test every 12-18 months. It is surprising the difference that even very early cataract development can make.

Many years ago very experienced coach told me that if you get to 40 and aren't wearing glasses for shooting then you probably should be.

Rutty

Astigmatism correction for my rear sight lens holder is actually easier than it is if the lens is in glasses.

After the lens is inserted and trapped by screwing in the rear iris, the entire lens holder screws into the rear sight and has a knurled collar that acts as a thread lock. So adjusting astigmatism is literally just loosening the knurled lock collar (no tool needed), then rotating the entire lens holder assembly to get your axis correct, then re-tightening the lock collar.

The comment about cleaning is a fair one. Trapped inside the holder, the lens is a lot less likely to get dirty in the first place, but if it does, it needs to be disassembled to be cleaned, and might shift your zeros slightly on re-assembly.

Personally, I can run a season between cleanings for an inserted lens, though for glasses they need cleaning weekly due to handling.