I've completed and passed both IAM and RoSPA and honestly I cant tell you which is 'better'.
My personal view is that you will get a huge amount out of both, but whichever you choose the quality of training is VERY dependent on how good your observer/tutor is, how committed they are and how you get on with them, and the trouble is you cant tell that until you've tried both. I had a few different ones with both and the difference was huge. If I was doing it again I'd actually consider getting some professional training.
I did find IAM was much better organised than RoSPA at a local and national level.
As for insurance don't bank on getting any reduction they save me less than £1 on my annual premium and I do shop around at each renewal.
