I am on my second Navman fuel unit. The first one didn't suvive the hose pipe, although it does have a rubber washer in it. However it was easy to fit and did provide a reliable figure of how much fuel we were using. I don't have fuel gauges as the two fuel tanks are triangle in shape to match the bottom of the boat. Pastimo did exchange the whole unit under guarantee, so no problems there, just need to be a bit more careful when washing it down and will fit it with sealant this time. Not bad for £155 and it only took a week to arrive with the chandlers from Plastimo.
They won't work with diesels as alreay mentioned because there is now way of monitoring the return line, unless you can send the return fuel back to the fuel filters instead of the main tank. Would this work ? or is there a reason for the fuel needing to be returned to the tank. This is one cause of moisture by the way as the fuel is warmed from the engine. Need some Soltron.