Did an Outwood to Leeds return this tea time to ride on both units. From a passenger perspective, they will be seen as a big improvement on the 321/322 units. Having 2+2 rather than 3+2 seats, the seating capacity is slightly lower than the units they are replacing, although I suspect more people will actually use a seat - there are too many 'XL' size people for 3+2 to be used fully. Legroom is much better too (was never normally a problem for me before, but I know it was for some!).
On the two sets I travelled on, the PIS was displaying adverts for the new trains on one set, while the second it was working properly, displaying all the stops. Noted the wording on the priority seats which said 'for people who are disabled, pregnant or less able to stand' - the latter is important as there are a multitude of reasons why people may not be able to for a significant period. It does need people to be good enough to give up the seat if required though. On my second journey, the guard did a manual announcement on departure from Leeds, explaining this was one of the new trains on its first day in service - a good PR move in my view.
The seat backs were fine in my view, but it needs some softer padding and better cloth below, particularly in warm weather when you're in shorts! Not too bad for a short journey though.
Acceleration seemed good leaving Leeds towards Ardsley, but unit caught up a Leeds-Sheffield service which had departed 5 mins late. New stock isn't going to improve timekeeping if there are other trains in the way...