Apple in chatswood does prostate massage. I tried it with her (my second experience, with the first time I tried a long time ago from a jap lady in Burwood). I'd say go for it if the girl specialises in it. A lot of men say it takes acouple sessions to truly appreciate prostate massage as you have to be really relaxed.

Make sure you clear you bowels and eat plenty of fibre before you take a shit... You want to try reduce the smell as much as possible.

Edit: but to answer your question if you're missing out? Who can say really. I think it's a different type of pleasure.

Girls experience clitoral orgasms differently to G spot orgasms, so the argument is there wether or not to try it out.