To start using some unregulated operation like 'AirBnB for cars' I would need do be paying virtually nothing as an incentive. And, from the examples I've seen so far, this is no way the case.
Also £100 is not their standard excess, so you're paying for the reduced liability. (Also, they like to tell you every time in the hard sell that the £1,000 excess is for each and every incident and the full amount will be taken immediately... ?! Not sure how true that is)
However, they have the most branches in the UK of any rental company, so they're often extremely convenient.
In theory then, I'd be better off taking the bigger risk but there is also Murphy's law to consider.
Maybe I have been lucky but I've found them to be much better than the alternatives and a lot more laid back about stuff like fuel levels and return times.
I don't drive much these days so I don't want the hassle of having a transferable insurance policy.
What I'm really saying is I'm happy with renting from an established company and it's going to take more than a small cost saving to tempt me away.