Please note that I was once the Special Markets Manager for Bennett and that I have no direct experience with QL Volvo Interupters, except from a competitors point of view. So that's where I'm coming from.
Tab vs no tab:
No boat "needs" tabs. They will float and move without them. All boats are designed to run best on an even keel within a certain bow up attitude. Any good tab system or interupter will help maintain this optimum "comfort" or "efficient" attitude (if sized correctly)
Either system will allow the vessel to run more efficiently, especially when used with speed info (gps) and fuel flow info. As noted a push of a button vs asking someone to move. Also, loading changes. Fuel is used, ice melts, tons of fish come aboard, beverages are consumed. Wave and wind create a dynamic environment and a vessels ability to adapt to maintain an efficient attitude typically results in a more comfortable and efficient ride.
Been around a long time, military uses them. Proven concept. Works on different principle than tabs.
The Science between the two systems (tabs vs interupters) calls out that tabs work better at slow speeds. Interupters need more speed in order to start working. if the goal is to plane comfortably at slower sppeds to stretch fuel Tabs should work better.
They both create lift at the transom, although through different science.
Interupters from QL should be easier to install because there is no pump to install. A Bennett pump is smaller than a 6 pack of tallboys.
Both systems need fairing blocks (for a B31) and both need dash switches and wires run from transom to dash.
Reliability and longevity:
Bennets have a 5 yr warranty. There is one moving part on the transom and the electrical component (pump) is mounted inside the boat. Most problems with a Bennett system can be fixed without hauling the boat. There are Bennett systems on the water that have been in service continually for 20+ years in salt water that are still operational.
QL Interupters are electrically actuated at the transom. Their long term reliability is still being tested. Like Lenco electric trim tabs, they count on seals to keep electric components dry.
Marine growth does not affect Bennett systems, the planes can be painted with antifouling per paint company guidelines for underwater metal and the actuator can be painted without any special priming.
Interupters do have the advantage that there is nothing sticking out the back of the vessel. Instead there are "planes' that stick down vertically from the transom. For some this may be an important factor.
Just a few comments from someone that was pretty close to the subject, hardly objective but then, I told you that.
Soundown Ft Lauderdale