Fair enough summary. The only one with any meaningful performance/ handling improvements is the 512M; but the looks are just odd. Change for the sake of it.
No, the M is the same mechanically as a TR. The only difference is that the M has titanium conrods and revs a fraction harder.
TR and M both have the lower mounted engine and same suspension dynamics.
Early trossa wirh tubular control arms are just dire, later trossa with 16" wheels and pressed arms are better, but until the TR came with 18" wheels all trossa are poor in comparison... But a tr is still not great!