The rental bikes provided are OK-but-not-great, I considered taking my own bike but didn't, and in hindsight wish I had. But the rental cost is just a rip-off - these bikes are £500 new (and no doubt a chunk less than that if you're a tour company buying a job lot of them), so paying a third of the new price to rent one for under two weeks is excessive. I can only think that they assume that customers won't want to ship their own bikes, and that therefore they can charge what they like. I've no idea whether "they" is Exodus or the local operator, but it comes to the same thing - being blatantly ripped off doesn't really engender repeat business.
I booked the single supplement, as I have on several other Exodus trips, but on this trip it was all of: expensive, weird, and poor. Expensive - just as a an extra % of the tour cost it was easily the most expensive I've paid, but I decided to go ahead anyway. But... on 3 nights I was in completely separate, and significantly less nice, accommodation than the rest of the group. This is just weird - all I wanted was a bit of privacy, I wasn't expecting to be punted off somewhere different. With hindsight I'd say the supplement simply isn't worth it, and that the company should review how they're choosing the accommodation - until/unless they change something I don't think it's worth it.
Final context statement to go with those two comments - the trip in general is good value, but these two things significantly detract from that assessment.