I stumbled upon this while watching Justin Johnson. You need to get used to it, but once you have it is really handy. You can play fully, and sometimes using a slide. Planning to use this to learn the 7 nation army Justin Johnson version.
It is a bit heavy, but not overwhelmingly. Fit very good on the finger(wearing on the middle finger). The spring is really good on it, doesn't squeez your finger but sits really tight. You can play 2 strings at the same time with it. It has quite a mellow tone to it, similar to a ceramic slide.