I experienced major head shake while riding chopped out nasty whoops for the first two years I rode my K5.
So, I had my suspension rebuilt for my weight and riding conditions and the head shake I experienced all but went away except for at the very upper end of top speeds. Even then it isn't much and I have never rode any MX tracks where I was able to get my K5 in 5th gear riding wide open
While the steering stabilizers work great, you may be masking the real problem.
If you have not visited a suspension specialist (Or, you are not one yourself) you might want to talk with one first.
If after getting the suspension dialed in you are still having problems, then by all means get a stabilizer.
.02