Yes - there are pages and pages on this topic on this site
It's not that bad - you don't have to pay back 25% at the end - but the tax man may want their share of the tax savings on the amount of the %25 you don't pay.
Eg. You buy a £1000 bike and pay £600 for it.
At the end, you pay your emloyer 5% (£50) to take ownership.
Taxman says 'you should have paid £250 for it! You made £200 tax-free there'!
And then claim the tax on £200 - which would be £50-£80 depending on tax bands.
So you pay about £700 for a £1000 bike.