Review on Uxcell Bracket Aluminum Extrusion Profile Industrial Hardware for Brackets by Shane Minter

They're not terrible, but they're not great either. I had to sand the edges to get them to sit evenly. It wasn't a big problem, just a few minutes on the mill. If you just want to make something solid you can use them out of the pack, but if you want square ones you'll need to undo the edges so they sit flat. Otherwise they are square and solid.