I have had the Donkee 2-speed for two years, and no problems. I use the Donkee at home for extended sessions, and use the spinner at the proshop for "quick and dirty" convenience.

I'm sure that the Vertex is a fine product, but evaluations against the Donkee is not an apples-to-apples comparison. The Vertex is a single speed motor that runs at 435 RPMs. The Donkee is a two speed model that operates at 570 and 850 RPMs, respectively.

The Donkee advantage is huge and cannot be rationally dismissed. Having a high speed (850 RPMs) for cleaning/polishing provides capability that doesn't exist in the Vertex. The high speed provides for the generation of heat necessary to truly clean the cover of a ball. Given that a spinner will be used for cleaning/polishing far more often than refinishing, I'm constantly amazed that this is overlooked.

You will not appreciate the difference between working with a generic one speed and versatile two-speed unless you spend considerable time with both. The limited (and manageable) vibration of a Donkee is a small price to pay for the much greater capability of the unit.
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"You want the truth? -- You can't handle the truth! "

I own a 12 lane center.  In my shop, I have a 2 speed Donkey spinner.  If I am resurfacing a ball, I have to wait about 3/4 the way through the job to let it cool down (it overheats).  Depending on how out of balance a ball is, the darn thing will just about jump off the bench.  I have thought of securing it, but I have not yet.  I used to have a single speed Jayhawk and I still miss it.  The 2 speeds are nice, but not worth the vibration.  I do like the splash gaurd though.  If I were using it only at home, the Donkee is OK, but if I were buying one again for a pro shop, I'd buy the single speed Jayhawk.
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TOON