thoroughly recommended. Instead of pounding it for an hour once or twice a week, I went down today, had a good half hour/forty mins of solid workout and have come back to my desk all refreshed. I'm going to do this every day now.
It's a bit like gcse bitesize...instead of cramming, do little bits each day and it breaks up into manageable chunks. Plus you dont lose time after work, nor feel knackered all day if you go before work.
All in all, lunch gym is where it is at.