I have owned 4 boats and my most recent 6.5 meter half cab has them fitted. Personally I find them an excellent feature. It seems if you have a high profile boat with cabin that can get pushed in a wind or in certain sea conditions the ability to be able to level the boat is fantastic. I was given some instruction on how to use them when I brought the boat and had the first ride. I would get them again on a similar size or larger boat in the future.
I also spoke to a person from Barcrusher at the boat show. He very knowledgeable and helpful. His advice was for trim tabs over 6m.
Cheers