Well, I picked up those mobile bases. I wish I hadn't.
I assembled one per the instructions. The pieces looked nice and the assembly was easy. Without scrutinizing it too closely, I put it under my little Grizzly G1035 shaper and immediately noticed it was leaning. The base isn't level. The brakes also don't positively engage. One little shove and they're undone.
I've been known to misassemble things, so I carefully put together the second one and it has the same rake to it. There is no way to adjust for level and it seems stupid to have to shim your tool to get it level. It's enough of a PITA to just get it into the base by yourself; you shouldn't have to fart around with bits of plywood.
I guess I got what I paid for.