Different opinions and different strokes. Someone will say the mains purifiers filter out (say) RF noise, another will point out that hifi equipment already does that, so why bother and so the arguments go on.
Simplest thing to do is, as igglebert said, get a hold of some, try them out on a loan basis from a dealer and then either buy or return. You might have to hand over some return postage if there isn't a suitable dealer nearby, but other than that, the risk is minimal.