One of the reasons why apple decided against having a touch screen in the mac book air was that it would make the laptop top heavy and horrible to use. I've used a few tablet pcs and apart from the HP DV2 range, they have been awful to use in terms of ergonomics.
I guess down to personal taste, but I would rather have a BT keyboard and ipad official case than one of those. But I would strongly suggest its a case of try before you buy.