I run my own company, and therefore had ready access to this scheme since I was both the employer and the employee, but I actually decided against it altogether.
Now, this was a couple of years ago, so you'll need to check whether what I say still applies, but this is what I found:
You have a twelve-month agreement where essentially the company buys the bike, and you then pay £x per month to lease the bike off them. The "x" covers the cost of the bike, but there is a tax saving to be had.
But I think you need to look at what happens at the end of the twelve month period. My understanding is that the company, not the individual, actually owns the bike. So in order for "you" to end up owning the bike, you'd need to buy it from your company (i.e. more expense). And when I looked at it, HMRC (the UK Tax authority) were making noises about the company having to sell the bike at a "fair market price". In other words, its not reasonable to take a £1000 bike, then to say that after a year it is only worth £10, or some ridiculously small amount.
Now, as I say, this was a couple of years ago. At the time I decided that the scheme was a bit half-baked, and to steer clear of it.
But I think what I'd be looking for now is to see some clarity on what happens at the end of the twelve months, how much you would need to pay to actually make the bike yours. Whether there were now concrete guidelines in place, or whether it was all as woolly as it was when I looked.
I think if looking at the different providers, that would be my defining criterion.
Sorry, I know this probably doesn't directly answer your question, but hopefully it'll give you some idea of one line of questions to ask the different providers in order to allow you to make your own decision.