I have an MK-390 and it works fine. I'm sure you're going to get several comments along the lines of "save for a Gen III" and that's dandy if you're looking to spend that much $$$ - they really are that good. But I don't use mine enough to justify the extra cost.
I can't tell you the difference between the 350 and 390 off the top of my head, but here's how my 390 works:
It has a removable rubber seal over the objective lens with a pinhole in it which allows you to use it when it's light outside (restricts the amount of light entering) so you can sight in during daylight - if I remember correctly, there's a time limit on daylight usage (10min?) before you need to shut it off to rest. It uses a weaver rail. The muzzle flash has not been an issue for me.
Yes, light can harm Gen 1 optics, but this one has a rubber cover over the front of it, which helps with that significantly. There is an IR spotlight that mounts on top of it which helps with illumination, and the range is ok.
I don't know what your setup is, but I was using it for hog hunting at night in Texas. That means feeders. I found that the night scope was fun, but it's heavy and unwieldy on a rifle. I ended up taking it off the rifle and using it as a 'spotting scope.' I put 2 or 3 of those cheap solar lights from home depot around the feeders I wanted to hunt at night and used the night scope while stalking within range of the feeder. Then I switched to my normal binoculars and a good quality scope. The lights aren't very bright, but they provide just enough illumination to see what's going on. On very dark nights, seeing the crosshairs was a problem, but with good moonlight and little to no cloudcover, this was the best setup I came up with. I've heard good things from other guys that hunt pigs at night about using scopes with an illuminated reticle to go with the solar lights, but I haven't tried it.
Here's the short version of what I just said:
1. Gen I scopes are fun, but difficult to use effectively (weight, quality of the picture, range) And they are very dependent on ambient lighting conditions (i.e. if it's cloudy, they aren't very effective)
2. For less money you can buy a few solar lights to put around your feeder and use your 'normal' daytime hunting rifle/scope and a pair of binocs.
I am by no means an expert on this stuff, but I did a fair amount of research before I bought mine. And I stayed at a Holiday Inn express last night.
YMMV - good luck with your decision.
