well
I own both an FX and a BTT and they both are easy to tune although the FX seems to be able to idle without loading up at all which I have never seen before.
The are both reliable no issues with either needed resizes at about the same time although the FX took a little longer to break in.
The FX has more bottom end and that is what I like and so I consider it a more all around engine although the smooth powerband of the btt and top speed help out on outdoor tracks. Fuel mileage I cant tell any difference.