I went with Adrian Flux once; I needed insurance sorted quickly, using my mobile just before boarding the train, and expected there would be no hassle. There wasn't.
However, come renewal time they were massively uncompetitive, wouldn't budge on price, and I haven't bothered with them since. I've been with Admiral, multicar, for the last five years, chopping, adding and changing cars pretty often, and never had any hassle either. Added to which, come renewal time I can never find the same cover more than a few pounds if at all cheaper.