After printing and using trustfm's filament splicer joiner with moderate success I decided to see if I couldn't improve on a splicer so that I could get consistent repeatable splices. I used mdkendall's Parallel Jaw Pliers as a base for the design. Modified the jaws to what you see here.

Using the same procedures as in trustfm's joiner I'm able to get consistent splices. After splicing I remove the PTFE tube from the left jaw and then sand the joint so that is passes smoothly through the tube. I've also found that in order to achieve a good splice that both ends of the filament being spliced need to be straightened so that the ends line up (and are parallel) with each other. I used M3 socket head cap screws throughout and a couple of screw caps from 3DPRINTINGWORLD.

Added a revised left side jaw after hearing about GreenDot's issue with the fillet.

Video link courtsey of Greendot
https://www.thingiverse.com/GreenDot/about
https://www.youtube.com/watch?v=hecs7q0hdLc