Are rovers picky about oem relays or will aftermarket work just fine?

 

Any good quality relay will work on these. No worries about aftermarket here- but do go with good, name brands.
Ford/Motorcraft relays are actually a good, high quality, affordable choice and what I often try to source. That's often what's already there anyway.
Case in point here with a 40A FoMoCo (fuel pump I think) relay from a 2008: