The ready heat shrink image in your post has incorrect link (but I loaded it and it looks good).
I understand the technique but they take too much work
So I leave them for where I actually have to use them. In most places they are installed on terminals which go onto the open terminal block anyway, so there isn't much point in sealing. I do places that are exposed to moisture, propane locker of course etc.
Even heating while spinning the crimp & wire between your fingers and KEEP THE TORCH MOVING!! I just installed over 40 heat shrink crimp connectors in the last five days and every one was done with my mini butane torch, I prefer my heat gun but in 40 crimps I ruined none...