I used the one on Touring Plans.
I’ve had about 90% success with it over several years. I’ve been unlucky in some cases because some restaurants just don’t see many cancellations (experiencing that with Storybook Dining this trip, just nothing for a party of 2) and sometimes I’m looking for ADRs for a larger party (over 4) which likely lowers my chances. A couple of times I got a notification for the hard-to-get ADR for several people, but didn’t make it to my laptop in time before the opening was snapped up by someone else.
But I’ve also gotten close to what I’ve wanted most of the time. Including a table for 4 at Space 220 next week during a busy time of day. I was so happy I didn’t even care that I was woken up by a notification text on a Sunday at 7 am lol.