Hi Nigel,
I've been using Jam Origin Midi Guitar since the early Beta days and as a guitar player, IMO this is the best $100 I've spent.......especially being a non-keyboardist. The tracking and responsiveness is excellent. There's a bunch of really good threads in here (Software) with some great tips on setting up.
Support is also excellent from the developer. Regarding sales, I haven't ever seen the price change from $99 since it came out. Highly recommended......