Basically at Sheridans you pay £30 and have the option of going in the room for a blowjob (called a blow and go by them) or going in the gloryhole instead. The general expectation for both is you don't take all of your clothes off, there is no sex, and that it will take less than 15 minutes. In the price you get OWO (at normal discretion) and until recently you sometimes got CIM (not sure if that will be a definite extra now or not, but best to assume not). If you like blowjobs, either option is good value compared to indie's offering 15 minute non penetration sessions and compared to other parlours. I find that most of the blow and go customers aren't particularly picky about which WG they get, they just want a warm willing mouth.
No idea what the price for the Czech hole would be, seems the parlour is keen on the idea of not just the WG being the one one her back instead it being the punter on their back with a variety of people (but 99% probably WGs) doing things to them. They do have quite a few sub punters who that might interest. They also have a few bi punters, they used to (and might still) do bi-orgies on sunday mornings (usually 3 punters & 3 WGs in one room).
And I've also seen:
Punters in reception being asked to watch other punters in their room (having sex with a WG, being dommed by a WG).
Punters paying to watch a WG and other punter during their booking.
One punter joining another mid way through a booking for a bit of MMF fun.
A punter paying for another punter to join the WG while they get dommed.
So, I don't think the Czech hole would just a case of sticking one of the regular WGs in stirrups for 9 hours and letting a procession of punters bang away at her. It seems like there would be a number of scenarios that might interest the kinkier of their clientele.