I did my IAM Skills For Life after doing my BikeSafe with what was then Central Scotland Police. Best thing I ever did for the bike. I of course realise that the IAM isn't for everyone, and I also know there are a few right nob'heads in the IAM - just as there are in pretty much every walk of life.
That said, I know plenty of guys and girls in the IAM who are bloody amazing riders, and I've learnt a tonne of stuff from them, including doing track days and slow mo days - all with excellent instruction and help - I really can't fault them
Compared to riding schools that can charge a small fortune for advanced riding courses, the IAM Skills For Life is currently £139 - a fraction of some courses. I highly recommend it - and if you get an observer you just can't get on with, you can ask to be assigned a different one.