I like the tees because I'm in upstate NY and last year my display was under at least 6" or we had pouring rain. Waterproof connectors are important....
You always use a Male plug at the beginning of the string and a Female at the end of the string, just like regular lights. the DIYLED Tees are setup...
I think you will get a lot of differing opinions on this one. I've seen people inject in the middle and/or the end. Personally, I talked to a friend...