I've owned this for about 7 or 8 years...basically from since it came out.

The best thing about it obviously that it enables you to add sounds to your guitar that simply couldn't not imagine before...and it can be damn handy.
The worst thing is that the tracking is slow and ghost notes can occur. This means that if you're not careful or you go too fast or strum too hard or not hard enough then you will get weird notes that were not quite desired. You can set the sensitivity of each string, though, to avoid this in most cases...takes some attention.

This was the first MIDI guitar system i tried and it's not surprising because before this there was virtually nothing. I think there was maybe the GR-50 and GR-1, and they were slower etc. This one could have benefitted from the expression pedal...you get with the GR-20 ! But you can always add your own i think.

Beware that the female output jacks are laid out & shaped in a way that will NOT let you use Neutrik jacks. You'll need something thinner!

The sounds in this are quite amazing, although i wouldn't use most of this for anything else than impressing the mates...
If you're careful, you can use the synth pads (which are VERY dynamic) to great effect, and if you put them through a good effects processor then you've got some fantastic sounds at your fingertips...
You can also use this as a regular MIDI expander for your existing keyboard! You can have 2 layers going at the same time, which is pretty cool. I used this with my shitty PSR-90 to make it into something acceptable.

If you have a Godin LGX (midi, electric and electro-acoustic separate outputs) you can have your regular electric mixed with the electro and then have a piano with strings via the GR-30. Now THAT makes a difference!
Also, you can do your solo through your electric amp and have it layered with 1 or 2 wild synth sounds.

Overall, i think it was a very expensive piece of equipment (i paid 4150 Francs, ie 625 €) but second hand it's probably quite a good deal now. If you use it. And put your mind to it, you really could!

The piano & organ sounds are quite good, the double bass sound is not bad either, and if you stick to the middle of the range you can use strings & trumpets and even trick people into making them think they're real.

I use it for one year. I like the diversity of sounds but Any vsti plug-in makes better today, this card, although having returned services is exceeded. For the same price it's better to look towards good vsti... The world evolves!