A buddy built one of these and the issue was the seats being integral to the table on a relatively small (round) base. Unless it was on perfectly flat surfaces mere breathing was manifested by more crosshair movement than desirable.
He did such a nice job on the spool we ended up pouring enough concrete to provide a flat base and fastened it to the concrete. It solved the stability problem but by that time, we decided that dimensional lumber might have been an easier way to go.
It's still around and still in use after almost 20 years.