"head to head" comparison?? Ohhhh boy.

Every boat we have had used the same manual head except the Islander, they all had relatively inexpensive Jabsco units. I believe all were original factory equipment as well. All seemed to work just fine, no leaks, no issues, no repairs ever required. The Islander had a more expensive unit, it was an older Groco. It didn't work right from the day we got the boat, never seemed to pump right, recirculated the black water as you described and always filled to the brim if you didn't get the seacock turned off PDQ. Never ever had that issue before with any other boat/head. One of my Islander projects was to upgrade the Groco to the latest and greatest version which I thought was a pretty cool way to do business. I bought the upgrade kit and did the project over the winter. Come spring and a reinstall, there was really no difference in anything that I could tell. In all fairness to Groco I never rebuilt a marine head in my life so there was the possibility of pilot error for sure.

FYI, our current boat, the IP, also has a Jabsco head, or at least a head with a Jabsco electric conversion done to it. This is our first electric and I can definitely see why they are becoming more popular. The built in macerator and pumps work extremely well. How will it be 5 years from now? No clue, sure works slick today though.