Re: PVS-15 and PVS-21 info
Yeah, the ANVIS 9s (F4949s) were/are developed for aviation, however they are seeing a lot of ground use now that they are being fielded to certain units. Mounts & battery packs have become ruggedized for them as well. The actual unit itself isn't nearly as hard use as the 15s are, but I suppose it all depends on what you are going to use them for.
The 9s have screws on each side that allow you to move the individual tubes left or right for positioning them over your eyes perfectly while the 15s are more like a binocular...if that makes sense. I like the 9s in this respect over the 15s, but it's also the weak point or where they are most fragile.
I'm happy with mine, I use them hunting, 4 wheeling, etc..
The 9s are cheaper, but if you are doing anything <span style="font-style: italic">serious or something that will bump and knock them around</span>, go with the 15 for the durability.