I was curious about this too. So I looked through all 24 pages (using a page search for "ego". I found one reviewer that said it wouldn't work on his ego. But I found probably 4 or so that said they worked fine. It could be that the lower mah egos wont work, or some batteries won't work, but I'm thinking most of them probably do. Of course the battery won't last as long, and its recharge cycles might be reduced.
I agree with JpKrHk, the 1.8 ohm are probably a wiser choice, especially for smaller egos like the 650 or 350 mah. I've been using 1.8 ohm single coils but I've ordered some 1.5 just to find out :)