I really question the need for these DC variable speed pumps in protein skimmers nowadays. To me this is just another gimmick the skimmer manufacturers are coming out with in order to have those that want the latest and greatest sell theirs and buy a DC pump version.
I would be very interested to know how many Diablo users, or any other variable speed skimmer pump users actually use their DC skimmer pump at anything but one speed all the time in normal operation?
Use the feed mode button, OK, but I have a feed mode on my controller, so I have that covered. Need to turn the flow down a bit for a while, a ball valve does that as well. Rising sump level, well I have a float switch in my sump that turns the skimmer pump off if the skimmer section water level gets too high
The DC skimmer pump craze really seems more of a manufacturer driven thing with no real benefits, except a higher price and something else to go wrong.
Skimmers operate on the principle of a steady, regular flow rate, and DC pumps seem an unnecessary complication with no real application in a skimmer setup. You adjust skimmers via water column height and/or the amount of air entering the skimmer. As theses DC pumps only have a few preset speeds, they are not even continuously adjustable, and you could do better adjusting pump flow with a gate or ball valve in the first place.
I am not commenting on their reliability or perhaps their application in a sump return pump situation, just in their use in protein skimmers.