My grandpa tied his boots the same way for 60 years even after velcro came out, and when his hands got too stiff to pull the laces he just stopped wearing those boots. Twenty years later we found three pairs of the exact same boot in his closet, all worn the same way. He wasn't wrong, his way worked, but he never once asked if it still did. The part that gets me about your story is the kid just nodded. He didn't push, he didn't argue, he just went back to work. That means he already figured you had a reason, even if you didn't. The hard part isn't learning the new tool, it's admitting the old one was maybe just a habit wearing a skill's clothes.

Laughed at the part where you ripped out two courses on the first day with the thing. Nothing says "worth every penny" like tearing down work you already did so you can do it again, the right way. That 1/4 inch would've turned into a wall that looks drunk from 50 feet out by the time you hit course 20. String lines lie to you on long runs, they sag and stretch and nobody notices until the whole thing leans. So yeah, you're justifying the expense, but with evidence, which is the best kind of justifying. Bet the laser paid for itself before lunch.