Certainly, not hard for spammers to break, but as long as it doesn't have widespread use, they won't bother putting in the effort.
But this can be said about almost any Javascripty custom trick, and there are ones that no effort from user and don't have accessibility issues beyond requiring JS.
Certainly, not hard for spammers to break, but as long as it doesn't have widespread use, they won't bother putting in the effort.