Just had the pleasure of my first trip on a 755, the 0652 from Attleborough.
I sat at one of the raised table seats above the Jacob's bogie in the second coach. Lovely smooth ride, lots of window views (I didn't mind the window film).
Engines couldn't really be heard, a bit of vague rumbling in stations and a distant sound of thrash when accelerating away. A bit like being sat in the first or second coach of an HST. This for me is the single most outstanding feature of these trains, no diesel engines thumping away under the floor. A nice peaceful journey.
I planned to have a wander through the power unit on the way to the facilities but as it turned out they were located in the coach I'd sat in, so will save that experience for another time.
Very impressive performance, both speeding up and slowing down. Sat at each station longer than was normal, and arrived into Ely several minutes early. I imagine it's a fun unit to drive!
Minor niggles.
The wifi didn't work, logged in as usual, then my phone refused to connect to it again. Not had this problem before with GA wifi. The mobile signal must be attenuated to some degree by the window film as it dropped from 4g to voice only a lot, and at places it wouldn't usually. So connectivity was a bit poor.
The sink in the toilet needs looking at. You have to hold your hand to one side of the water spout, so it shuts off as soon as you try to get your hands wet. After about the fifth spray it refused to play any more. The soap dispenser is a pull rather than a push which is the wrong way round to my mind (and I don't like having to grasp something like that for obvious reasons).
There were a couple of panels with annoying rattles but fortunately this subsided once the engines throttled back.
Guard made a manual announcement on the approach to Ely. It sounded odd, kept cutting in and out and clipping some of the words. I deduced it works like an aviation intercom, and mutes when there is no speech to minimise the amount of static and general noise played through the speakers but it needs the squelch adjusting.
Rail/wheel droning noise was a bit louder than I was expecting. Might have been due to where I sat.
But these are all very minor niggle to me and are massively outweighed by the good features.
Also notable that the guard was always fully focused on and available forpassenger assistance, ticket checks etc without the distraction of door and despatch procedures every few minutes.
All in all it has to be the nicest regional train I've ever travelled on. Very impressive, lightyears ahead of a 15x and a decent improvement on a 170.