its not that they are on there good or not, its dry wire your gonna get from the raw copper wires being exposed to air. it wont happen over night but over time it will kill the wire and not flow current like it should.

solder is weather proof, it dont come apart if done right, the shrink tube will keep any air out at the end of the lug to the wire.

i like to cut my wire so the rubber insulation is sunk into the lug, then shrink tube it as well.

you can use a plumbers soldering kit, flux and solder costs like 5 bucks. the flux is a big part of doing it right. as that vid shows.