If it's free it's free!!!
I have these a lot, on salad, on toast or just as a snack or part of packed lunch eaten straight out the tin. They count for the 1-2 portions of oily fish a week you're supposed to aim for, for the omega 3. when I first discovered them I went a bit mad, but then learned that it's not a good idea to have too many as they are quite high in mercury. The NHS guidelines are max 4 portions a week (2 if you're conceiving/pregnant/breastfeeding).
Sorry to hijack - but easier to keep these in one place for future reference!! - is mackerel in curry sauce free too?