I was told about it ages ago but thought nothing of it, you just need to be careful if soaking parts with polished surfaces like hub flanges etc as it will dull them and take the shine off the areas that aren't rusty but yes I couldn't believe the results you end up with it just dissolves the rust like magic with very little effort.
Were did you guy's get yours from I can only seem to find it in morrisons but it is 97p for a 500ml bottle?