MJ - I see your point but but my limited exposure to Rotaxs in VLA in the training envoroemnt shows them to burn around 12 lts an hour and thats a hell of a saving compaired to an o-200 or o-235.
I also wonder if UL91 will cause a domino effect as if one school starts offering it then others will have to follow as they will not be able to compete from a price point of view.
Of course we could all just switch to C42 and then poor ASDA unleaded in and there has been a large drift in this direction over the last few years.