Cycle to work schemes are variable,
There are two main factors
1. Finance, someone has to pay for the bike up-front, a good scheme would build that in as you are paying RRP which gives them enough overhead to finance it for 'free'.. The poorer schemes will have quite a hefty charge for finance which comes off your savings.
2. NI Contribution reduction, this is down to the company, they can take that off the monthly cost of the bike (effectively giving it to you), or they may pocket it, or use that to pay for the finance to buy the bikes upfront.
Then the law changed in terms of how the bikes are 'transferred' to you after the end of the scheme, effectively the longer you own it, the lower the residual value, I think after 3-4 years that's effectively nothing, or a token fee (I can't remember the exact terms). Some schemes push things and will effectively give the bike to you after 12 months (maybe at a single months final payment) but they are administratively keeping that bike on their system and automatically writing it off 3 or so years later.
My first Scheme was ace, as a high rate tax payer I managed to persuade the scheme to let me have a Cannondale Rush 6 mountain bike for £1000 (RRP was £1400 but it was an end of year sale), I only paid £583 for it (that's tax saved and NI contributions), the company financed the bikes for free and passed on maximum savings, it was definitely worth it then.. However 2 years later some company came in and showed them how the company could make money out of the scheme, and that was it, the next bike I went to get was £1000 and effectively it would cost me £832.. I queried this with the Scheme provider and the very nice person in their customer services let me in on how it worked, our company was pocketing the NI contributions and adding a 14.9% APR finance fee on top, to which they got a kick back from the company because buying a bike at RRP obviously maximises their profit as well and offered 'incentives' to the company for each bike sold.. I made sure everyone was made aware of this in work and oddly that scheme got shut down 12 months later due to poor take up..