My wire version I used for straightening a rail that was already sitting in plane with its pair since the surface had been epoxy leveled, it was looking down on the wire from above so gravity wasn't an issue. Your setup will work for a single rail in 1D as you have it setup in the video with the laser firing down the rail but you couldn't use it for bringing things into plane as the laser surface is not flat enough. You need a really expensive lens for generating a flat surface, if you look up commercial products for leveling machines in this way you can see the price of the laser source, that is all going into the lens.