We did it last month and we were a party of 4. I know you can book it for parties as small as 1.
As far as good...we enjoyed it. The desserts were pretty tasty and quite plentiful. Tables area also assigned, so it's nice having 'your place' to sit and eat.
Everyone does crowd the rail come fireworks time, but there is plenty of space for everyone at the party to have a front row view on the rail...at least from our experience. My only real issue is that it's not my favorite vantage point for the show. i.e. you're a little bit off to one side of the castle. Still, it's a pretty nice view.
All in all, it's awesome to be able to avoid the insane crowds...which made it totally worth it in my opinion.