You can pick them up cheap second hand if you look hard enough and I see no reason why they couldn't be a QT tank depending on what fish you want to hold in them and what size you were thinking of. A 30L might be ok for smaller fish. I ran a 30L as a hospital tank and keep one as a spare now for such purposes - not that I have had to use it for that.Sorry for the hijack
Assuming that you're aware of the huge limitations of these tanks (thanks for the unbiased info by the way!), could you run one of these as a Q tank?