Meggy,
I used to have the Pro version, then upgraded to Ultra Plus pack last year. there is likely a lot of improvements on the sounds with the real band, etc, but honestly I still use the basic version sounds as the real band optino takes about 10-15 seconds to load a tune each time you pres play. That doesn't sound like much, but when you are trying to practice a tune over and over or 2-5-1 improv soloing, etc. that delay can become annoying.
If you have a MAC, I think
http://www.irealb.com is a much better bang for the buck. I use it on my iPhone and it really works well for practicing. For $20. it is probably the best value.
iRealB doesn't have any real tunes loaded on the program due to copyright issues, but you can go to the iRealB forum and down load 1200 jazz standards for free.