Yea, They suck. They are cheep crap. The outside burns before the middle solder melts well. The shrink wrap sucks and is thin crap. They don't hold good and some of the ones I tried the solder wouldn't flow well into the wires.
I am in the electrical trade (electrical controls tech) and have connected from #14 awg wires to fixing cut in half 4160 volt armor cables back together. The high voltage stuff is much more involved. But for low voltage wiring the best stuff I have found for sealing wires together is as following:
Use standard solder to mate the wires or you can use mechanical connectors, butt splices or such. I found that on marine stuff its best to solder even if you use butt connectors, fill them up with solder to keep the corrosion out of them. Before you connect them slide a shrink wrap on the wire that has a sealing glue inside of it. The item you have posted has seal glue of some type at both ends but the shrink wrap I refer to has the glue in the entire tube and it will ooze out the ends once shrank down ensuring a 100% seal. I have done 480v under ground wiring using this stuff before and sealed it twice over with good results. One tube on each wire in a cable and then one large one over the entire cable area that was spliced. That works good on multi wire cables. Here is a link the stuff below I use:
It is sold by the foot at different lengths and can be cut to the desired wanted length. Also sold in different diameters. Make sure it is the type with the glue additive in it to ensure 100% seal.
These types have the seal glue:
Standard moisture seal tube, Extra thick moisture seal tube and chemical & uv resistant moisture seal tube listed all have the water proof sealant inside the heat shrink tube:
https://www.mcmaster.com/heat-shrink-tubing