I did have the OAS 7 yes. The sounds are very good and have a lovely warmth to them. It's hard to describe, but it's something only Wersi can do. They have that certain sound which tells you it's a Wersi straight away. There are the few exceptions as on all keyboards but not many bad sounds at all. The internal styles are quite bland, typical organ stuff and not in the same league as top end arrangers, but they are more than passable and certainly not like the ones you hear in the MS
The T2 and Yamaha styles do not need converting if you buy and install the OAA software which isn't cheap. I saw this in action and it does a very good job of playing them back. A little bit of tweaking is involved for some and although they still sound better on the T2 itself as expected, the OAA is leagues ahead of the other style convertors eg. EMC Styleworks doesn't come close to this.
It's a shame mine had faults as the machine was growing on me, but I wouldn't consider getting another because the VST's which I wanted to use are a right pain to get working. It's far easier if you are into VST's to use your PC and midi a keyboard to it rather than attempt to play them from the Wersi.