The "drop fins" capture water that would normally slip out the side increasing the efficiency of the tabs by about 25-30%. The edges of the tabs must be parallel with the keel to use these.
Bennett doesn't weld because it changes the properties of the stainless and could increase the rate of corrosion. There are a few manufacturers that insist on welding on tabs and in those cases Bennett does weld but then passivates the tabs.
Most Bennett Tabs can easily be removed for the "drop fin" mod by disconnecting the actuator and loosening the hinge screws into the transom. At some point the tabs will clear the locking tab and just slide out the side without removing the hinge entirely.
A little known fact is that on many Bennett tabs sold to Mainship the Actuators were restricted in their travel. Mainship did this to avoid bow steering and along with the minimum sized tabs on the Pilots this restricted the performance of the tabs. A standard Bennett Actuator travels 2.5". The modified Actuators travel 1.75". If you have a modified actuator there will be a label on the bottom of the lower hinge (where it attaches to the tab.)
Another easy fix for a little more performance is an actuator spacer. Bennet will give these to you for free for the asking. They are triangular and the same footprint as the upper hinge where it attaches to the hull. It is notched to fit around the brass nipple that carries the fluid and is easy to install, even in the water for most boats. You just back off the 3 screws in the transom, slip the spacer between the actuator and the hull, goop it all up, and re tighten the screws. Gives .5" additional travel down but does away with the - angle Bennett recommends.
Dougcole, Mainship used 12" x 48" tabs with dual actuators and 1' upfins for the entire run of 400's. You might check if you have restricted stroke actuators which would be the best way for you to improve performance.
Most of the above are "fixes." There's nothing better than a bigger tab, I had 12" x 42" on my olde '78 MSI and they were the difference between planing or not. There are ways to install bigger tabs on most boats, and the single actuator is standard up to 12" x 42" tabs.
Good luck,