I actually haven't been using it a lot lately, since I'm in the middle of finishing an "electric free jazz" album that's almost all fucked-up power trio stuff. One of the tracks features some guitar synth, but the rest is all guitar/bass/drums. The next project will feature lots of synth, both guitar and keyboard.
However, I have played around fairly extensively with the Axon, so here are few pros and cons.
--Tracks way more accurately than the Roland gear. Not perfect, though. The lower strings are still problematic, but at least they're usable. You'll still encounter a few glitches, though you can reduce that by working closely with the string sensitivity and MIDI parameters within the Axon. There are a few problems I haven't been able to dial out, such as natural harmonics at the 5th and 7th frets on the lower strings interfering with accuracy and causing little octave ghost notes.
--Faster. Way, way faster. If you set the string sensitivity high and play carefully, it will trigger as fast as you can play. Obviously this setting is prone to more glitches, but I haven't had to adjust my playing nearly as much as I did with the Roland GR-33. You still can't just "zone out" and play, but it's much better.
--Much more configurable than the Roland stuff. You can set the various parameters to both your instrument and your playing style. You can also set up patches with different parameters, so that, for example, you have a very string-sensitive patch for soloing and a less sensitive one for chordal work.
--Can be set to so that each string is on a separate MIDI channel. This improves accuracy and allows for all kinds of crazy playing using multi-timbral synths. You can also set different "zones" on the neck to send on different channels. I use hardware synths and have gotten great results in separate mode with my Yamaha Motif ES, but have had problems with my Roland XV-5080 and JD-990 modules, which don't have the option of receiving MIDI on all channels simultaneously in patch mode. You have to go to the multi-timbral performance mode on Roland gear to use separate mode in the Axon, and that's a big old hassle. Using all strings on a common MIDI channel in the Axon isn't that much different, however.
--The Axon is not user-friendly at all. It comes set up to be somewhat usable right out of the box, but you have to do a lot of tweaking to get good results, and the menu layout and manual are difficult to decipher. The AX50 is editable only on a computer interface and is probably easier. However, you really have to know MIDI *very* well in order to get good results. Things like pitch bend information really affect the quality of your playing on some synth sounds, and you have to learn how the various MIDI parameters work. Pitch bend on the Axon doesn't just involve bending strings or using the trem, but also distinguishing hammer-ons from plucked notes, which is a huge part of my playing. Setting pitch bend to zero means that you have to pick every single note, but it also means you won't get any goofy accidental pitch bend commands when you are using a piano sound, for example.
--The Axon patches all send program change information by default, which is useless and a pain in the ass for me in a studio situation, especially since I haven't been able to get the program-change stuff to actually work properly with either the Roland or Yamaha gear. Whenever I switch to an Axon patch that I haven't modified properly, it always causes the synths to spazz out and switch to a seemingly random GM patch. Even my modified Axon patches still cause interaction issues whenever I switch to a new patch. In short, I still have a *lot* of MIDI communication issues to iron out, and it's frankly a bit frustrating. I can't say how well the AX50 would play with soft synths, but hopefully better.
--The tracking is sketchy on 5- or 6-string chords, unless you set the sensitivity very low. There is so much harmonic "cross-talk" when you hit a guitar chord, that even a good controller like the Axon doesn't know how to process it very well. Setting the sensitivity low means that the Axon ignores all but the loudest signals, but it also means you have to hit the bejeezus out of the strings to make it work. And you start to get omitted notes with the sensitivity that low. I don't know that there's a solution to this. It's just an inherent problem of pitch-to-MIDI conversion. Harmonically, guitars put out a very "dirty" signal that is always going to be difficult to convert into a proper MIDI pitch, and chords make that ten times more difficult.
I'm definitely planning to order a You Rock Guitar, since I would like a simpler guitar controller solution, and hopefully one that tracks better for chords. For soloing, though, having a 'real' guitar synth controller is probably still going to be essential. For example, playing a synth "saxophone" or "violin" solo is much more satisfying on the Axon than on the keyboard, because the Axon's ability to distinguish hammer-ons makes for much more convincing and life-like phrasing. Violinists also do hammer-ons, and sax players change fingerings during the same breath, which is strikingly similar to the effect of a hammer-on. Keyboardists have a much more difficult time replicating that.