I have never seen an Erasmic brush but I own two Wilkinsons; the pure badger, which is a prickly floppy and absolutely non-dense waste of good money, and the boar/badger mix brush which is not bad at all as long as you don't pay too much.
They also have a boar brush but that doesn't get much positive reviews here; I never used one though so I can't comment on it.
I have both. The Erasmic is actually a fine small-ish, short-lofted boar. Good and scrubby, breaks in quickly and then is decently soft. For only £3, you can't really go wrong. The Wilkinson boar that I have is, well, not so good. I may try it again and see if I am being unfair.