These are also a very nice product and you will never have to worry about them coming apart. I've tried to pull them apart and you end ripping the insulation on the wire the glue is so strong. They make them in many different sizes as well as ring terminals.
http://www.waytekwire.com/item/30980...RMA-SEAL-BUTT/
I think for an install that maybe seen John's method a much more attractive and professional way of doing a buttsplice though.