I use it for DD, have been using it since she was maybe 2 & 4 months? Has been fantastic for her! We still get bad nights here and there, but overall she has definitely improved!
Don't think I would feel comfortable using it on a bub that young, although it does just say on the bottle 'for the whole family' and doesn't state an age range.
Sorry I don't have any other advice for you, but if it were me I would probably leave rescue sleep until around 2 years..