I'd love to know why people have such an issue with ICR's. The only reason I can think of is that they replaced loco hauled sets.
Before anyone says 'you haven't used them', as of yesterday I've done 20,713.82 miles on the things, over 227 vehicles. I have had NO problem reading, writing, using a phone, sleeping, talking, listening to music or anything like that. Same with the Mark 4's. They are by far the best option for an intercity railcar. Yes you do get some vibrations and rattles from the engine, but compared to some in the UK you would hardly notice it.
The problem is not the stock but the track. One section that springs to mind in Monasterevin in the Down direction. Flung around at speed regardless of what you are in