IAM have come a long way in the past few years as their qualification at the top end have had a major overhaul and is now a match for the RoSPA (and in fact may even surpass RoSPA) grades.
I did my time as an IAM examiner and stopped because the standard was so poor with no retest requirement and it simply being a pass or fail. This is all very different now and in my 40 years as an advanced examiner there have been a lot of improvements to the testing of civilian riders at advanced level.
That's good to hear. I passed my test in 2007 and observed from 2008 to about 2013. Nice to see that none are stuck in their ways.