It's a bit of a strange perk really (they mostly are), the tax benefits roll upwards, so I have always doubted it does much for the bottom of the workforce. But then cycling (even cycle-commuting) is a very middle-class affair. As such most companies who offer the scheme are probably the employers of reasonably paid middle-class professionals.
I felt a bit bad (as really it's just tax avoidance, I could afford the bike) – but not bad enough not to – using it to get a Brompton, but it was a fair saving. I think I had to pay £30 to make it mine at the end. I did try to get another Brompton this year, but the wait to get one through Halfords meant we didn't bother this time around (the mothership doesn't offer it all year round).
It may encourage some people to cycle, of course, in which case I suppose it's incrementally beneficial. I've no idea how effective it is or the cost of the scheme. I suspect there's probably better ways to get people cycling, but given the governments we have, and the fact the blinds are always drawn down on their imaginations, often it's best to accept something rather than the usual nothing.