I ended up going with the Onyx Boox i62HD, for about US$150 + extras & shipping. Have been using it for a few days and am
very happy with it.
This puts it at about 3/4 the price of the PB622 (160 Euro), with clearly superior hardware (HD resolution + IR touchscreen vs capacitive on the 622). Although I
mildly prefer the PB software, they are sufficiently equivalent (particularly the fact that they both include FBReader), that this was a no-brainer.
Likewise, although I was
intrigued by the Wexler, and it is now being sold by a couple of stores, the newness (and thus untriedness) of the tech, combined with the lack of
detailed documentation (e.g. an online-available manual) or reviews and the US$350 (or thereabouts) pricetag made it a non-starter. Maybe in a couple of years time (when the tech has matured & the prices come down).