I've had experience of 170s which I think have the one of the best views going, shame that the rest of the train underneath is so rubbish (to put it politely), but even they had their foibles when coupling & uncoupling to a 15x unit!
458's in their original guise were a right PITA and they were always going wrong, even when they were 4 cars, they still have issues when coupling up today as 5 cars, so the argument of not having or having a gangway making the difference doesn't really stand up there I'm afraid.
Desiros are generally very good when it comes to coupling & uncoupling, like the old stuff with buckeyes & tightlocks, you can get the odd one or two which won't couple up and it doesn't help when you don't notice the kamikaze pigeon or pheasant in the knuckle hole when you go to couple up and subsequently gets turned into mulch when you try, but if they don't or won't couple up, especially at the principal locations where it's done on a regular basis, just call a fitter or "phone a friend" and do what they say.