It also depends how your employer treats the bike at the end of the 12 months.
I get a £1k bike under Halfords C2W, but can choose from a number of approved retailers (I managed to persuade my LBS to sign up to the scheme so I could buy a Cube from him rather than Leisurelakes which was the other option I had)
I pay 40% tax, and so save that plus a bit of NI.
At the end of the year my employer gives me the bike. HMRC treat that as a taxable benefit, and make me pay tax on it. They value a £1K bike at £250 at 12 months old, so I have to pay 40% of that as a further one off payment (£100) The bike is then mine.
I also have the option of giving the bike back to my employer and walking away. Yeah right!
All in all I get a brand spanker for about £680 with 0% finance.