The machines your talking about are the, Haus Machine, Cook Sphere Machine and I'll include the Storm Surface Factory.
Yes these machines produce a lot more uniform surface, they'll get flats spot out etc. They are really more for doing a resurfacing as apposed to just surface changes IMO.
Spinners are good for doing surface changes fast and if you follow all the steps you can resurface without messing up your ball. It's like a lot things it just takes practice.
Using a spinner how can one be certain the ball has been resurfaced evenly? For the most part from experience, spinner's have been around a lot longer in pro shops than surfacing machines.
Overtime you can get a ball out of round, you can get flat spots around the holes. If you don't learn to keep the pressure even, flip the ball to the different sides, do the sides the same amount of time, know that the top of the ball will sand faster than the side.
That's why once in a while take it in and have it threw on the diamond wheels on one of the machines to have it trued up.
Though I doubt most bowlers these days have balls long enough to get them to far out of round with a home spinner.
It's easier now most sanding pads have foam backing, that helps with keeping a even firm pressure. One thing you should have if using a spinner is at least one Taxi C.A.B. Block (Contour Abrasion Block) they are contoured to the shape of the ball for holding your sanding pad or paper.