Hi Kway
I've been a few times, they used to do a small (around 10-12 players) monthly walkon but I think it has stopped now due to low demand. They also offer a mixed paintball/airsoft/go karting day for punters, with occasional zombie themes around holidays.
It only has one field, which is indoor/underground and very small - more than say 8-10 a side and I can see it getting crowded, but great fun with lots of intense short ranged firefights, room clearances and a couple of sneaky doors/tunnels to surprise the other team. The marshalls have very creative missions and use different starting points for each game to add a surprising amount of variety with only the one field.
It's good once or twice a year but it can get a bit repetitive going more often, especially if you can't break through the main choke point on the field.
It's site paint only (clear paint as indoors) and relatively expensive - more so for punter days. Despite that I would say it's worth giving it a try if you can get your own group for the day, or enough walkons together.
Rob