I’ve never had even a single issue with Spectacle so not really a big deal to me that it’s no longer maintained. It Just Works, from my experience - with that said who knows for how long, I guess.
When I first saw Rectangle, I thought I saw there was one Spectacle feature it was missing due to APIs. I'm looking now and it looks like it has everything I use, which is great.
I’ve never had even a single issue with Spectacle so not really a big deal to me that it’s no longer maintained. It Just Works, from my experience - with that said who knows for how long, I guess.