[roger albert]

Those solder-filled shrink connectors are pretty poor.
They very often leave joints that look OK, but are fairly poor.
They violate the first rule of soldering, which is that the underlying
metal should be hot enough to heat the solder and cause it to flow and give good wetting. These, instead, see the solder melt (and sometimes the insulation) before the underlying conductors ever achieve the right temp. They're not absolute crap, but they're poor, misleading, and give a false sense of having made a quality joint. I can't tell you how many of these I've had to pull out and replace. They border on snakeoil.