The Tridentsim is absolutely brilliant fun and excellent value.
Sure its a bit tired (it is very old) but it works fine for practicing ILS SIDs and STARS etc.
The owner will also just let you lose on it and he won't insist on you employing an instructor.He doesn't hover over your shoulder all of the time either. I believe instructors are available who will prepare you for a Sim check ride to get you up to speed.
Comparing £70/hour to the £400 some charge for a 747 sim I know where my money would go.
Best thing is to get 3 or 4 of you together and rent it for a couple of hours each taking turns in the RHS and LHS.
Go and do it.