I don't see how this is the kicker's fault. This will happen with ANY type of rigid boom support of you do not have the boom end secured up and down. The simple trick is to dump the topping lift and run your halyard to the boom end. Snug the halyeard and mainsheet and you are sorted.
I don't agree with you, any other boat I have been on with a "rigid" boom vang the end of the boom did not bounce up and down 12" when going over a small wake. They seem to use an air piston that may be dampened.
The boom kicker held up the boom fine with the sail up, but once the sail came down it only required a couple more pounds to cause the boom to drop a fair bit. Any kind of small chop on the water and the boom was going into a 12" oscillation between the top of the bimini and the end of the vang.
It would not have been easy to remove the halyard and attach it to the end of the boom as I would have had to collapse the bimini to reach the end of the boom. Also I like to keep the sail ready to deploy when coming back in case the motor should stall. (Something my sailing instructor drilled into my head.)
After trying the boom kicker I put the the topping lift back on. I felt I had spent the money needlessly on the boom kicker and wished someone had pointed out these issues to me before I bought one. On my next boat I found some shock cord between two loops in the topping lift worked better and at almost no cost.
As I said in my original post, many people have boom kickers and like them, I had one and didn't.
Bob