It's a year subscription and it's absolutely worth it if you are seeing a bunch of shows and are flexible about when you see them during youe trip. I usually only go to NYC once a year and the number of shows I use TDF for varies depending on what I'm seeing but even one or two shows can save you over the $40 it costs for a year subscription. Last year, I got two Water For Elephants tickets that would have been $160 each on the website for $60 each on TDF just for example.
A lot of Broadway shows have been up lately. Regular ones recently include Gypsy, Sunset, RWHC, Boop, Smash, & Juliet, Stranger Things, Cabaret, Dead Outlaw, Floyd Collins, Moulin Rouge, Hadestown, Hell's Kitchen and The Last Five Years.