Well I can report that I ended up grabbing the cheapest option, a Dick
Smith-branded one for $40. Recorded a couple of snippets of TV to a spare
USB stick, and though there were a couple of minor stutters playing back on
the box itself, they look fine on my laptop.

The mpeg stream is saved into a .ts container file at original quality,
including subtitle & audio for sight impaired streams (though these were
empty for the snippets I grabbed). I thought that was an interesting
feature, even though I don't think the box lets you play them.

ADVENTURES WITH GOOGLE! On the Dick Smith product page they offer a
firmware update. Searching for the filename of the update indicates that
Teac and Bush have released versions of essentially the same hardware over
the past couple of years, at higher prices of course :) The Teac model JB
are currently selling for $59 seems to be different, but at that price I
can't imagine it would be vastly so. A search for what I figured was the
manufacturer's product number turned up wholesalers on Alibaba offering the
Dick Smith model, unbranded, but only for a few dollars less on massive
wholesale orders...

Anyway, first impressions are that this is pretty solid for a $40 HD set
top box with USB recording, assuming you don't want to be able to record
one channel while you watch another, etc. Glad I didn't pay more.