Resident swap is just really slow about removing the filled programs from their site. Definitely, they think it's to their advantage so to attract more customers. They rely on users to report it out of date. I've done it a few times and then they eventually remove the post after contacting the program to get affirmation that the position is indeed filled. Maybe some programs are also slow to affirm.. I don't know. I did an experiement and didn't report the path pgy1 position as out of date, and, it is still there. So, now I'll finish my little experiement and report it out of date now and let's see when they take it off.
But it is, indeed a legitimate site. I was also super reluctant to purchase the subscription, but, strangely, programs use residentswap much, much more frequently than find a resident...