I'm not sure about those particular Lenco tabs, but most of the tabs like that only power down. They are just spring loaded to make them come up. When you press the button to raise the tabs, a solenoid opens and lets the spring pressure push the fluid back into the pump. The problem with that is that in faster boats, the water pressure under the tabs wants to pull them down. The water pressure will overcome the spring pressure and the tab will start to lower while you are running. Obviously, this will cost some speed. At what speed? it depends on the boat, spring pressure, etc. I have seen it happen at 70 mph. I will not install them on a boat that will run over 80 mph. It could become dangerous in a fast boat.
The Eddie Marine tabs are pretty nice. I have installed several sets over the years. When they first came out, I had some problems with quality. They have since fixed that and the last few sets have worked great. I think they are worth the investment over the Lenco's. You may also want to look at the Dana Marine tabs. I am a dealer for both Eddie and Dana, so give me a shout and I will give you the best price I can. I look forward to speaking with you.