I stayed at Plaza on the River in July and would highly recommend it for family travel. The views of the river were nice and it was great to have a little extra room to stretch out. But being on the other side of the river is not ideal - feels a little detached from the more lively parts of the city and is about a 10 minute walk to the tube. Therefore I would look to the other more centrally located hotels (May Fair, Mercer, etc) if I were traveling solo or with a spouse.

BTW, I am gold via Club Carlson credit card. I booked 2 nights at Plaza on the River for 50k points in the studio. I put in for a room upgrade via the links in the confirmation email - was 27 GBP/night for a space available upgrade at check-in to a 1BR suite. When I checked in, they upgraded me another category to the 2BR suite riverview for the 27gBP.