I had 9 flights with Transavia (ever), never had any real issues with them when it came to weight/size or even getting the hand luggage on board.

Truth be told, out of my 6 Vueling flights, 2 times the gate staff was being difficult about the size of the trolley. And Ryanair 1 out of 2. So for a low cost airline, Transavia isn't all that bad.

That said I try to avoid LC carriers if I can.