Those really aren't great to use in places that see heat. The solder can heat up, reflow, and have the wires separate.

I'm a fan of butt connectors with no insulation over them. They're very slim and when covered with heatshrink line with adhesive, they're water proof.

Lots of OEs supply those connectors in their wire repair kits. I haven't seen any that supply those solder melt butts.