That’s a ThunderBolt port :)

It showed “Center / Fair” for me

You can only install 3 self-signed apps at a time, and they expire after 7 days. It’s meant to make it difficult for anything other than development purposes.

Thanks

Not always. It can be perfectly reasonable to implement something in a quick and dirty way to get it out there with a view to either kill it off (eg if it doesn’t get adopted by users) or re-write before it needs to be extended. The key is having the awareness when putting yourself in that position.