I saw a 55" TCL at BB this week- it's on sale for $299. Looked pretty good, but I would make sure it's not set up fro display- it's often called 'torch mode' because the colors are so hot (too high). The red color was too strong- ask them to set it up for home use and take a few minutes before going back to it to make any decisions.
I don't know that I would worry about edge lit, or not- How old are they? Have they had a large TV? If not, they may not like that size of a screen.
Whatever you get- make sure it switches from the ROKU apps to TV channels easily. If they have cable,