Since people seem to be lukewarm to the TV suggested by the OP, I did an Amazon search for 4K TVs under $600:
https://www.amazon.com/s/gp/search/ref=sr_nr_p_n_size_browse...
Anyone have any experience with the top TVs on this list? The top entry from TCL seems to be the leader, by far, in terms of average customer review, but the price point seems almost too good to be true: $379 for the 55' version, though that may have been a sale price, and the TV is currently out of stock.
https://www.amazon.com/TCL-49S405-49-Inch-Ultra-Smart/dp/B01...