I have some experience double bitted axes including the Iltis, Snow and Nealley, and an old Vaughan Sub-Zero.
The Snow and Nealley I got wasn't good. First, the head was ground really crooked so it looked like someone grabbed each edge and twisted them. Second, the edges were really, really thick and round. When I tried to chop with it the first time (before doing any work on it) it would just bounce off the wood. Third, the head started slowly coming off immediately and it wouldn't stay on even after I reset it and pounded the wedge in more.
I haven't had a chance to chop with the Iltis yet but it looks good. The handle is really generous and has a small shrunken part on the end for a hand to hold it, which I think is really nice. Also, the edge came pretty sharp and nicely shaped for good cutting and penetration. Also, there are some serious looking round wedges that look like they're really going to hold the head on. Lastly, I think they say the head is hardened to 58 so you probably won't have to sharpen it much.
The Sub Zero was my grandfather's and he got it sometime in the '60s or '70s. It has one hollow ground side and one thicker ground side. The hollow ground side is thin! Boy, it really penetrates and makes popping a large piece of wood out on every swing easy. Also, the steel feels good and hard (but not too hard), which I like. You can still get a Sub Zero but I don't know how it would compare to mine.