'A guy from wolf' with that kind of feedback is highly unlikely to be the individual who decided on the 'capacity' at Bunker 51.
Those complaining about prices should bear in mind the location, residential property in that area is worth over £13k per square meter right now.Let be conservative and say you get 3 hours play for your £30 and compare that to the laser tag at the same location which is £10 for 20 minutes if you pre-book. It's a sad fact that the cost of living is higher in the capital than the rest of the country, and that obviously affects the cost of recreation as well.
For me, living in London zone 2, it's way cheaper than going to the Mall (which I do enjoy). Half hour drive with free parking or £3 by the tube. Also means I don't have to get up as early and I'm home in time for dinner.
Back to the OP, I've played at Blitz once with Airborne. There was about 30-odd players, and I still enjoyed myself, however I can put up with a slower pace of play as I'm unfit and lazy. If you prefer better flowing games, then 20 is probably better, however with less players, if someone has to skip a round or doesn't pull their weight then there is greater impact on a teams performance.