I used this recently: Tapa-Circuit
It works well. Just replace an existing fuse with it. It has two fuse slots. One for the fuse you just replaced, to protect the existing circuit, and another for the fuse to protect the new circuit.
You need to find your own grounding point, but this beats cutting, tapping, and splicing as far as I'm concerned. I just grounded my accessories to a bolt under the dash. (Bolt has to go to chassis...)