I've used it. It's excellent. Works as advertised. Truth be told, I'm too cheap to buy it often, though. It's good if yr painting a sharp line next to an area that remains unpainted. But if you're painting trim or a wall, I found this technique with 'cheap' blue tape to work as effectively (granted it takes more time):
Say yr painting a chair rail white against a green wall. You tape the wall against the rail. Then you paint over the seam with the green wall color. This seals the edge and prevents subsequent seepage. Then you paint the chair rail it's real color. Comes out perfect.