Went to this restaurant with 3 friends before attending a concert at the SSE Hydro (which is across the road). Very busy car park, and just managed to get a space.
The restaurant itself is large and was packed on the evening of our visit. We all chose the pre-theatre menu, and were surprised by the range of food on offer - there were plenty of choices that we all liked, even for the fussy eaters amongst us.
The service was very quick - just what we wanted for a pre-concert meal. From sitting down to starting our first course, it was barely 10 minutes. The main meals were around 20 minutes after that. If this was a romantic meal, then the service would have been too rushed, but for the purpose of a meal before a concert, spot on. The food was hot, portions were a good size.
The restaurant was geared, certainly at the time of our visit, to providing a fast service specifically for concert goers. I can't comment on what service would be like on a non-concert night or during the day.
One small but great touch - the background music was from the artists that was performing at the SSE Hydro. Apparently they do this for all meals where there's a performance next door (and I'm sure that the SECC and Armadillo).
I certainly will be back next time I'm attending a concert.