It appears there are only 2 different sources to pick up a spinner:
Currently debating on picking one up from either from Ultimarc or GG....the Ultimarc I notice that there is no separate PCB required and it's all built into the spinner were as for the Turbo Twist 2, a separate PCB - connection board is provided. So 1 point for Ultimarc which will be cleaner for installation.
Sorry, but that point was awarded in error.
A bit put off that for the Ultimarc, I have to purchase the bottom weight and a control know separately - $99 vs $69 for TT2.
Both of them have optional fly-weights.
The TT2 Energy Storage Cylinder (ESC) is a $5.95 option.
I'm very happy with mine, especially since a button wrench will fit over the ESC to snug down the TT2.

I'm not sure how 'good' is the default included knob offered in the TT2, but was thinking of getting the black rubber one - anyone know of the diameter sizes of the various knobs? I know that the standard included one is 1 1/4"
The skirt on the TT2 regular knob measures 1.33" and the grip measures 1.32" -- not bad, but the ridges can be annoying when you play too many games of Omega Race.

The skirt on the TT2 Rubber grip knob measures 1.48" and the grip measures 1.32" -- much more comfortable grip and a better feel than the standard knob IMHO.
The only down-side to the standard and black rubber knobs is that the bodies are plastic, unlike the higher cost (and higher quality) premium knobs -- don't over-torque the setscrew.
If you're considering the steering wheel option, spring for the 7" model.
Scott