I assume Mary Anne is referring to the ssscat. I have purchased four of the devices. They are currently sitting in a closet unused. They did not work for me. One of my cats was totally unfazed by them. And only one cat is still deterred by them
Furthermore, of the four units, three failed within a month. One was replaced under warranty. The air canister has a limited life and replacement is expensive. It's a gamble that it will work -- an expensive gamble. If the cat learns to be deterred by the whistle alone, then I suppose it's a good solution. But my experience is that result was obtained in only one out of three cats.
Deterrents will work with some cats. They won't work with other cats. This person has said they've already tried everything they know of, and it hasn't worked. So I assume this cat is one of the determined ones, and I really don't see any point in spending money on more cat deterrents that will most likely prove useless. That's the basis of my viewpoint.
BTW - I have taught them to stay off the counter while I'm preparing food, and to stay off the kitchen table while I'm sitting there eating. But that didn't involve static or active cat deterrent devices. It involved consistent, repetitive action on my part.
I suspect the main reason Mary Anne's cats respect her wishes not to be up on the two places she mentions is because there isn't anything up there to catch their interest. And I'll bet she provides plenty of more interesting alternative high places for them that they prefer. Two principles that can also be applied to kitchen countertops.