This appears to be a variant of a technique known in the research literature as Quikwriting [1] (a type of FlowMenu [2]), which you can still try online [3]. There hasn't been much in the way of evaluation of Quickwriting, but one study found people's initial performance was around 4WPM, increasing to 16WPM after five hours of practice [4].
I haven't used 8pen's implementation (so I don't know how their version differs), but I imagine it has a similarly steep learning curve.
Agreed, I demo'd Dr. Perlin's Quikwriting for the Palm which back in the day of capacitive touch, one had to put a plastic film template overlay of the glyphs. While novel and innovative, it was unfortunately overshadowed by other keyboarding methods, fitaly et al. That said, 8open efforts while admirable need to be tested against stock 4.2 swipe with autocorrection which i found most satisfactory above all other methods. ymmv