He can do whatever he wants. Nobody has to follow my suggestion. Maybe he'll just pay a shop to install, and save himself the hassle. Not that hard to install a wire run, but if you've never done it before, and have no electrical knowledge......it's best to ask for help. And not online. Maybe a buddy who does know a little more.

I remember seeing plenty of Jeeps & off-road vehicles where guys didn't use relays either. Just toggle switches. And their wire connections were twisted together and wrapped with tape. A circuit is pretty simple. Especially since we're talking about low voltage. You can get away with twisting wire together and wrapping electrical tape. Until years down the road when the glue on the tape dries. Same reason why twist nuts are okay, until road vibration and bumps take their toll. Just as much effort involved in making a good connection the first time around.

Back when people mounted lights on steel bumpers and steel roll cages, a lot of lights were self grounding though the hardware. One guy's light was loose, and kept flickering on & off. So he grabbed a couple of wrenches, to tighten down the nut & bolt. Somehow he was wearing a ring, and a bracelet on his right hand. The handle on the wrench was metal, metal jewelry, metal bumper, metal body parts, metal zipper on designer jeans......another path was created for the path to ground......it was pouring down rain......you can bet that I'll never do that again.

If everything works right, then nothing bad will happen. Safety precautions are only for things like wrong wire gauge to handle the wattage & run length, arc faults, ground faults, and voltage spikes. Some people want to over engineer. I see electrical panels with circuit breakers, but there's still a fused disconnect for manual switching. It's like having sprinklers, a fire extinguisher, and a water hose, when you already have heat sensors and smoke detectors. Same reason why you install shut-off valves with gas lines.