I've used them on 4 boats and had excellent results with them every time.
The largest boat, however, was a 20 ft. Gulf Coast ( Boston Whaler copy )
with a 150 hp o/b engine. All 4 boats...had jack plates and/or engine
extensions.

Most people say that they work well; however, they cost you some top end
speed, and that tabs are better for many applications.

Do a search on www.Google.com for Bennet; Lenco; and Smart Tabs, and you
will find many discussions, both pro and con, on these three different
approaches to tabs.
--
RichG
http://groups.msn.com/CarolinaSkiffOwners