Jerry
I have never owned a boat (except 13' outboard) with out tabs. I always use them. On my 25 Chris (Catalina 9'6" beam) on the bay they were great. I would adjust the tabs if someone would shift sides or move fwd/aft. On the 31 there is not much changing when one person switches sides of fwd/aft, but 2-3 makes a difference. But when necessary I do adjust them. I also tend to run bow down, as I believe the bow is designed to cut the water and if it is coming out you are tending to pushing more water, however this may contradict what Paul said about less wetted area and less friction. Also if I run my engines up to 2700 RPM with no tab and start adding (lowering tab, bow down) I gain 200 to 300 RPMs. So I am decresing load on the engines but creating more friction, but not pushing water from mid hull.
I also like being able to vary attack angle during rough/changing sea states.
My father had a 27' Owens with a 327 Chev. first year with boat, no trim tabs, did a trip from Delware River above Phila to Chesapeake City in C&D Canal, ran out of gas entering Engineers cove 49+ gallons. Next Year installed Trim Tabs, same trip 35 gallons.
I have always had Bennett Trim Tabs. I like the installation and never had a problem. I was on a boat with Boat Levelors, twin engine flybridge wood with many people, running at high speed and control solenoid stuck for one tab, boat took hard nose dive to one side, took a little for Capt to figure what was happening, wasn't pretty. I also don't like the exposed hose on the boat levelor tabs.
I agree with all Lee had to say. I wouldn't own a boat without them. My boats always had them when I bought them. I talked 2nd PO of my Commander to put them on her before I ever thought I would by her. He got a deal on Bennetts, I think their 18"X9", I think they're a little small but they do work, so it may be just a visual thing, and my 25 Chris had bigger tabs 24"x9".
Rob