Yossi was huge for us in 08/09, but that's a few seasons ago now, and I doubt he's become better with age. Personally I wouldn't ever consider buying a Chelsea reject - look how swimmingly our last one went. They sell for a reason, and that reason is usually that the player can't cut it.
If we were to get him, I certainly wouldn't expect him as a regular starter, but I still believe he has a lot to offer as an impact sub. He brings a lot of energy and creativity to the pitch.