Interesting question Brian, and one I have pondered recently as it looks like I will have to undertake ERD before I can enrol on the BSAC SMG course, and doing them back to back is not an option for me with loads of trips and family holidays coming up
I can only speak having done quite a few dives to 50m on weak nitrox [I can't tell you exactly as I don't remember
] and not having done any trimix dives I have nothing to compare them to, but TBH I am not aware of suffering any problems, and feel quite comfortable at that depth on predominantly air, I'm a bit woolly on the surface so maybe my rapture is not so pronounced
but I am looking forward to eventually diving on trimix and will then edit my posts as necessary
Safe diving,
Steve