I bought the unit to use with my Multiac guitar. The GP-10 doesn't come with the 13 pin cable, you need to have that. I bought a cheaper version of that cable online for $16, and it works just fine.
I loaded the drivers into my Mac, set up my synths in Logic, and was up and running in 10 minutes.
(Note to my sales rep: I mistakenly downloaded the drivers for the GT-10 first; tell us not to do that!)
I was anticipating a delay between the guitar and the synth sounds, and it is pretty noticeable.
But for my application, I either trigger pads with soft attacks to expand the timber of my chords, or use the guitar just to enter midi notes instead of having to use a keyboard into my DAW.
My technique is good, I play a lot of open chords, and it tracks my playing very well with just a few artifacts, most if not all of which are in the low notes.
To groove with a sound with a fast attack is kind of limiting, you need to get used to anticipating the beat.
Also, the 'synth sounds' in the unit sound cheesy (do people still say that?) to my ears, especially compared to Absynth or my G-Force mellotron.
There is no 5 pin Midi out to drive your old hardware synths, but I found a custom box for that purpose on the V-guitar site. Also, there is no Midi in to get more foot control over the unit, but perhaps you could do that through the computer.
I used just the effects with my electric guitar using the 1/4" input, I also downloaded the software to control the effects. It's a really nice, well thought out piece of software, very easy to use.
The effects in the unit sound great, (not surprisingly), and you can easily change the order of effects and the parameters, and store patches with just a click of the mouse.
My only observation is the effects themselves don't sound too 'deep', even with the effect level at 100%.
But then again, I'm comparing them to my collection of killer stomp boxes, some of which actually cost more than this unit. The amp emulations are good, and definitely useable for recording.
I'm not going to go into the live limitations of the unit, but there are additional options of adding footswitches and expression pedals, and I'm sure they work perfectly.
But to get the most out of a GP-10, you really need to cart around your computer to edit and lay out your patches and your set, because you can't just kick multiple individual effects in and out.
Plus, the software is so good it makes editing parameters in the unit a true drag.
All in all, for the small size, great sound, computer interfacing capability, and price, I feel I've made a great purchase. This is definitely a unit I'm going to use a lot. Oh, and it plays nice with my other effects on the floor.
I gave it a 4 star rating because I'm not ("WOW!, Blown away!"); it does exactly what I need it to do and then some. I really expected it to be this good, and it met my expectations.