The bat makers don't have to abide by anything, there isn't a law against making the bats, just using them. If the bat maker fancies testing out a new idea/design they why not!
Don't see the issue with them personally, at the end of the day it won't make a blind bit of difference in a game unless you're a top level player timing the poop out of every ball faced anyway - I wouldn't use one but I wouldn't kick off if I saw someone using one (and I have seen many)