I'm also in the UK and on Clearstep, and have been for about 2 1/2 years! My experience of it has been mixed - to be honest after so long with the aligners I'm pretty fed up of it, and my teeth don't look particularly straight yet so I reckon at least another 6 months before I'm done...
On the plus side, they really are invisible and you don't have those nasty attachments that Invisalign users always complain about. After a few weeks the whole teeth-brushing thing becomes second nature, and you even learn to relax a little about leaving them out for longer than you should, e.g. on a well-deserved trip to the pub (don't tell anyone else on here I said that)
Another downside is constantly having to go back to the dentist to get impressions re-done for your next set of aligners, but I guess this depends on how long you're going to be on Clearstep.
But overall I'm glad I'm having it done and I'm really glad I don't have train tracks. If you get fed up just remind yourself why you're doing it and how great your teeth will look when you're done!