Cupa,
I just spotted this old thread. Sorry if it's a bit late.
I was an instructor with RoSPA for 3 years. I packed it in as it's a thankless expensive task, but thats another story
I have done the The RoSPA and IAM courses. They are both worthwhile, but you will find that the RoSPA is the higher standard of the 2. The RoSPA has retest every 3 years, which means that you are always upto date. The test is harder and longer with RoSPA as well. RoSPA use Serving Police officers for the test. When I did the IAM they used their own people for the test.
The IAM has their own book. RoSPA use the Roadcraft book (the police 'Bible')
RoSPA also has the diploma if you realy want to get into it. This is the closest thing a civilian can get to a Police class one rider. You need to get RoSPA gold before you can go for that.
There is a large Boring old fart factor with both groups. Some of the observers/Instructors can be a bit stuck up with both groups. I was 25 when I became an intstructor and I can say that the born agains who made up most of the pupils had a big problem with my age. They realy do not like to be given 'advice'.
The IAM makes money from the courses. RoSPA is free, you just pay the Police for the test. It's £30 in Manchester at the moment, although it may vary in other areas.
You will learn lots about observation and positioning, defensive riding etc. You will learn safer more efficient overtakes etc. Which will make you probably a bit safer and smoother, but not faster. Although you will be getting from a to b faster as you will make more use of the roads.
The other factor you make like about RoSPA is that they will allow a more sensible aproach to speed. They will never put it in writing but if you 'momentarily break the speed limit' to make a safe overtake for example, you will not get a bollocking (As long as you can explain why you needed to select that speed).
Observed runs usualy last 2/3 hours with RoSPA and not the more usual 1 hour with IAM (this may vary in some groups). Which means that I always used to make a proper run out, to Wales or the Lakes for example. When in National speed limit areas, you will be encouraged to go 'as fast as you feel comfortable' and bang on the limit in 30,40,50's. I know that the IAM dont do this, they will not allow any speeding.
If you have any more questions or need to know where you nearest RoSPA group is let me have you're postcode.