Depends almost entirely on how solid the slider mechanism is, and how nice the keyboard feels to type on. TOHKBD is cool, but IMO it's pretty horrible to type on because you need to exert so much force to press some of the keys. And obviously the slider mechanism isn't as solid as a mechanical slider (not that they could have done anything about that, since it was a TOH). I think the neo900 idea of re-using a lot of the quality components of the N900 was sensible for this reason. You don't want to have a device that looks good on paper but in reality has a dodgy, wobbly, flimsy feeling slider.
I would gladly pay 400 GBP (currently 466 EUR, who know for how long) for a device exactly as per Chen's specification.