I built https://sslping.com/ to help monitor website TLS/SSL security and certificates. It has 300 users and checks almost 7000 servers every day for TLS problems. It's a little like SSLlabs server test, only much faster (5 seconds instead of 2 minutes), plus the tests are recurring every day, and you receive the diff if any. It's always been a joy to receive thank you emails from users, or adding new features for us…
And of course 5 seconds is how fast it should be :P
EDIT: Wondered what constructive criticism I could add, in case it was useful.
I guess the one thing I'm thinking of that isn't there is a cert tree breakdown, showing the cert structure in an easy-to-read format (which can be done xD), showing the trust root used, etc etc. I'm also reminded of all the little incidents that have happened with different SSL providers, and wonder whether people would appreciate seeing "you're using XYZ cert provider, here are controversial things about them". A feature like this would require careful presentation to work at scale though. Now I understand why you took the "go/no-go" super-simple route!
I also discovered (after noticing the fun URL query approach you use when you type in a domain) that disabling JS results in a white screen. That's common nowadays, so no comment.