The seats shouldn't in principle be that much of an issue - they don't differ massively from Grammer E3000s, and I've spent three hours in those going down to Weymouth and three from Crewe to Bletchley via the wobble. The problem is the stupid metal bar on the original, thinner, fabric covered cushions, and that the back is a bit over-contoured for short people so they force tall peoples' shoulders forward.
Oh, and the manky drab grey interior with that nasty green stripe. The interior of the LNER Azuma, despite being otherwise identical, is so much more homely, much more like a Pendolino but with brighter lighting to suit those who find Pendolinos a bit dingy.