Those connectors,,, uggh, I've used those.. I wasn't happy with the long term . They work, but didn't last.
The tubular butt splice work okay.. but a good stripper really helps, well, DUUHH, don't they, though?
And then they crimp the splicer onto your wire.
And that can be nice,,
http://www.amazon.com/Klein-Tools-11063W-Katapult-Stripper/dp/B00BC39YFQ/ref=...At Lowe's, not in tools, but in back, with the electrical supplies, conduit, breakers,I spent around twenty-five..
But they just strip.
Crimpers are part of electronic cheapo, usually red handled,wire stripper/crimpers.
You can get a set of the common gauge connectors and a stripper/ crimper at harbor freight.
I'm not a fan of wire nuts and vibration.
I usually solder and heat shrink, but, seems aircraft guys are less thrilled about that. I've never had a failure.