To answer the question adequately, you first have to define your primary use of a spinner:
(1) To clean and polish on a regular basis?
OR
(2) To refinish or alter the surface?
The majority of bowlers will use a spinner for (1) the vast majority of the time. I'm a cover alteration junkie, but (2) is not something you generally do every day.
So if (1) is your primary activity, it's hard to beat the Donkee. When it comes to cleaning or burning in polish, there is no substitute for high speed friction (and consequent heat generation), and here the Donkee excels. The Donkee operates at a high speed of 850 RPM's, while the Vertex spins along at 435 RPM's. Do the math, and here, the choice of a Donkee is a no-brainer.
The other side of the coin is refinishing. Most of the complaints about the Donkee are about vibration, and you certainly don't want the ball jumping around when you're trying to alter the cover. Personally, this hasn't been an issue. I use a CAB, and the Donkee vibration level has been manageable. I've never had a ball of out of round. However, others say the Vertex and Innovative models have less vibration and are easier to work with.
Like most things in life, there are trade offs here and you have to decide what activity is going to be most important.
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"You want the truth? -- You can't handle the truth! "
