West Anglia customers on twitter seem to like the new trains. Aircon especially. Even though I know many here view the longitudinal seats as a 'downgrade'.
The 710s are nice trains, a definite step up on the 378s, but I'm sure all the passengers would consider longitudinal seating a downgrade, especially at a time when the overcrowding which led to this decision does't exist due to lockdown!
I must admit as a regular user I do like them, even with the longitudinal seating. Realistically the maximum journey time is not a problem to be sitting in this way, and if you're at the far reaches of the line in Enfield or Cheshunt, you have got alternative options if sitting in this way
really bothers you (Great Northern from Enfield Chase, or Greater Anglia from Cheshunt). I have overheard people who have caught one for the first time mentioning how there's considerably less seating available than the old trains though.
I have however certainly appreciated the air conditioning (and even the charging points since I usually get on early enough to bag those seats). They do ride nicely as well, and the 315s and 317s were certainly ageing so everyone I knew was past ready for an upgrade.