You must be talking about a 4-2-4 select that disconnects the front diff so you can run in 2wd. A DGL is completely enclosed in the front diff and ensures both wheels will always spin, even if one is off the ground.
Thats where the problem is. I talked to HL the other day and once the few that they have in stock are sold thats it.Highlifter made a unlocker before the warn 424 came out. It had some design flaws. One of them was the teflon bushing wearing out on the shift fork. Very few still run them.