It's a con. I don't mind third party companies that actually provide a decent service, but they don't take away any of the hard work. In most cases payroll still have to action the salary sacrifices. Finance still have to monitor the repayments and balance the control accounts. HR (or someone) still have to collect and ensure that hire agreements are correct and signed.Not a fan of the cyclescheme variant like other people though.
All the third party do is restrict which bike and which stores you can go to and take a big slice of the pie for the priviledge of identifying your own personal tax saving entitlement! Not only are the repayments slightly higher but they also take you to the cleaners with the disposal fee, or delay ownership transfer for years.
Halfords don't take a cut... they run a decent website that makes signing up and applying an absolute piece of cake. It always used to be a bummer that you had to buy Halfords or hope the special order line can source your specific request, however this year they've started pointing you in the direction of your LBS if you have specific requests enabling you to literally 'hire' any bike you desire (under £1k). Because your employer still pay full whack for the bike initially, the way they deal with the ownership transfer is then entirely in their own hands and can be done as reasonably as possible for the employees.
If you're prepared to knock up your own hire agreements though, and pay multiple LBSs instead of one halfords invoice, going it alone is a very realistic option.
It always helps massively if you have one or two enthusiastic people in influential positions however, and in my experience the schemes that operate the most effectively are the ones that have someone who's prepared to take the time to understand the scheme workings and the different options and translate this to the decision makers. If your work doesn't currently have a scheme there's no reason why that person can't be anyone on here.
It's a shame that those who have had bad experiences are so quick to rubbish the scheme as a whole, without understanding that if implemented correctly then everyone can benefit substantially.