I use one of these in my nitro car(as do many of the guys round here) and I have had no glitching problems what so ever.
I use a Hitec Lynx 3D w/Spectra module
So I'm going completely crystaless, and still no glitching. Not even in nitro.
As for whether its worth the money....I would say only if your racing and you have to deal with a lot of freq. changes. If you happen to use a channel that no one else ever uses, then the XXtra would be kinda pointless....
Otherwise....yes it is worth the money.