OK so it looks like most of the supported cheap devices around doing this are driven by the video4Linux UVC driver (kind of as if their webcam feeds) or the Video4Linux usbtv driver.
However there are many chipsets which have issues under GNU/Linux some can’t be made to work or others require strange hackish userland drivers.
Also to make matters worse most of the cheap ones are Chinese jobs, which don’t have formal model numbers or product lines; and are prone to sudden change of chipsets and therefore often seemingly lie about their chipsets on product pages. Youll notice several such devices claiming to be UVC with Amazon reviews angrily stating they are not.
However most of these chinese devices are trying to clone a common family of once popular devices known as easycap. There are three or four chipsets in this family of clone; and one hits the sweetspot of being available right now and having very good support in kernel (3.19 and higher). This is namely the UTV007 chip.
Linux TV wiki on this family of devices: Easycap - LinuxTVWiki
This lead me to the Easyday DC60 which seems to be advertised in some places as having the correct chip.
Which if you find is available from a bunch of retailers for dirt cheap, and has atleast one less than year old Amazon review of it working with Debian.
So I may gamble with it. Its a cheap gamble, and hopefully the manufacturer hasn’t rotated to a different dirt cheap analog video capture chipset yet.