At work our tool room has several of these that were fabricated in house. They are on about the fourth version of them now. The first was like the ones on the Ebay ad, pulling on the adjusting screw. That don't work. The screw turns when you don't want it to, and the angle you are pulling at is wrong, and the threads rip out of the vice grip handle. The rod of the slide hammer needs to be welded to the top of the vice grip, and not parallel to the handle but raised up slightly. Ours now work much better than the versions similar to the ones on Ebay, don't waste your money on his, make your own.
Charles