But how much of dealing with the claim is up to the agent? One of the claims about companies using Colossus is that it gives the agent no leeway when handling claims. I'd also hate for my experience to be up to the agent - what happens for example if they were away on holiday when an issue happened?

When I moved from the UK to the US it was rather bizarrely up to individual agents discretion as to taking me on. In general everyone quoted you the same rates as a 16 year old who had never driven before, because you had no insured time in the US. But one agent was prepared to take non-US driving experience into account.