To save you the trouble and the money:
-Velocity is a bit rubbish now.
-Hero really is that bad! One member on last year's meet managed the first drop and corner before screaming "This is
<REDACTED> poo!". I can't think of a single redeeming feature. The queue's bad, the wait's bad, the ride is janky in the bad way, it's just a bad idea in general
-Mumbo Jumbo is easily one of the worst coasters I've done. 2 cars on a circuit designed for 4/5, with dispatch waiting until the last car returned to the brakes.
-Kumali *used* to be a good example of an SLC, but now it's as bad/worse than infusion. Coupled with the >5 minute dispatches means it's pretty lacklustre. And it only has one train, so you're in for a wait! Make sure you wave at the electrician at the top of the lift
Though to be honest, rubbish ride hardware is only half the story with FL. The biggest problem is operations, with huge waits for no reason on most rides. It's a small park, so I understand that their operations aren't going to be the same as Phantasia, but they're charging Arsenal prices for Pickering FC matches. Kumali and Velocity only have the one train, Mumbo Jumbo has 3 or 4, but only runs 2. I've sat in the garden on a boiling Saturday in the middle of the summer holidays when the park's rammed for one of the music events they put on, and timed Kumali at 10 minutes per train. They were really hammering them through on Mumbo Jumbo too, getting 250 pph.
I've also heard stories from recent employees that really make me not want to go and to stop other people going.
For vouchers, keep an eye in the gazette & herald, they sometimes run 2-4-1's in spring/summer, I think the Daily Express had one too last year