I mostly agree. But I’ve also priced it both ways and while you spend as much on a pre-made unit, and found that what I would be building has better coverage and penetration, as well as efficiency. At least for the smaller ones I’d build. Also there is the modular aspect. I can make two 2x2’ units for the same price as a pre-made 2x4’ unit. Those 2x2’s can be moved around in different ways.
And I do enjoy making the buggers. I would suggest only wiring fixtures “in series” vs “in parallel” for safety sake.
Also, invest in a AFCI/GFCI outlet. Will trip if any arcing happens or there are grounding issues. Can save a life and a home. Same for premade units. Just because they are remade doesn’t make them fool proof