You can see all the LED illuminators 940 and down ...or at least every one I have seen you can. The 940 is dimmer than an 850, but you can see it....and yes, the 940 has less range. Hogs will bust on these from time to time, but it isn't a deal breaker to keep someone from getting in the game.
A digital scope with low end thermal monoc is a fairly popular setup. Just expect that ID at any sort of range is more difficult with the lower end, low mag, lower res. monoc. Depth perception with thermal takes some getting used to.
I would personally stay way from clip-ons. Just my preference.
UltimateNightVision.com offers what is advertised as the only true return to zero mount for ATN scopes. http://www.ultimatenightvision.com/ATN-ThOR-QD-Mount-p/dloc-thor.htm
I have never trusted any scope to remain zeroed after removal and re-installation, but I just want to err on the side of caution.