This was a previous Ministry of Defence testing facility so the both the location and the design of the tunnel are a bit incongruous when compared to modern tunnels.
Pros:
It's a big big tunnel and powerful enough for freeflying in too. Great for 4 way as most blocks can be flown in there.
The vibe is really laid back. Once you've signed your disclaimer you can do what you want in there, pretty much. They not insistent on you following the IBA progression.
There are excellent onsite facilities, a bar, a good cafe (the full English breakfast is recommended), accommodation that's great value for money if a bit basic, a flowrider, climbing wall (good for kids but not a hard-core bouldering wall or anything) plus spa, gym, pool, sauna and steam room. There's a gear store and they are also dealers for boogieman if you want measuring up for a new suit.
Cons:
The air is much more turbulent than modern tunnels. They're pretty open about this but it does take some getting used to. It's well worth doing a few minutes solo before group flying if you've never been in there before just to get the hang of it.
The burble at the door is quite bad and again, it really pays dividends to carve 4 or 5 feet above the net to avoid it.
Other stuff:
The fan is straight above the top net and can be seen from the flying chamber. This makes the strength of the air greater as it gets higher. It's not uncommon to get stuck on the top net which is really weird. The corollary of this is that just above the net the air is a bit weaker so again it pays to fly a bit higher than you would at a skyventure tunnel. There's no diffuser.
For higher wind speeds it takes a bit more time to get up to speed than modern tunnels.
The location's unusual - it's not really near any population centres being an ex-MoD site but there are a few nice pubs close by. If you're into 1950s ex-military derelict architecture then this place would be amazing [;-)]