The BTX eyepiece is only four hundred more dollars than the ATX eyepiece, if you can afford the ATX, you could probably swing that BTX by just saving for another few months.
At one point I had a pair of 10x50 EL's, 15x56 SLC's, and a Razor 65mm spotter. I liked using my 10's the best, bright and wide FOV. 15's were okay, I just personally didn't like having two pair of binos. I actually found more game with my 10's than I did with 15's. So I tended to carry my 10's and a spotter, but still hardly ever used the spotter because of what others have said. The Razors are good, but not great, I would just use it to get a little better look at things. Got rid of the 15's and upgraded the spotter to an ATX 65 last year and got the 85mm lens for it last month. Since I got the ATX last year I use the spotting scope A LOT. Its incredible how clear the 85 is even at 60x, really enjoyable to use that thing. I also learned how to glass with both eyes open or just take off my hat and use the bill to cover one eye if I am using it for a long time.
Point is, the better glass in a spotter will make a difference in the quality of your experience using it, BUT, there is also an element of personal preference. Some guys hate spotters and love 15x binos, other guys think having 15x's is dumb and carry the spotter all day. I'd say just get the ATS or ATX on a deal, maybe on black friday or one on the forums, and use it for a while. If you like it, keep it, if you still don't like it, they hold their value well, sell it and get your money back.