My wife has a 500 with the factory cab and is really happy with it. I think it is a pretty nice option, and it's too bad they discontinued the cabs for the 500. Perhaps they just didn't sell enough of them. There is a sticker on it that says its actually made by Curtis exclusively for Kubota. On the Curtis cab site, I see they still make the cabs for the larger RTVs, but don't list the cab for the 500 anymore.
We got the recall done also, and in addition to sealing up a few openings into the cab a little better and replacing the hand brake boot (as mentioned in earlier post) they also replaced the tail pipe. The dealer had the recall kit on hand and only took a couple hours for them to complete the work.