Mostly visual differences, the Hical unit uses a slightly more aggressive feed angle for the magazine. Essentially everything else is the same, though the actual mag latch is slightly lower on the newer Hical adapter. The installation is the same on either one, though loaded rounds using the Hical adapter seem to feed higher into the chamber due to the aforementioned change in angle. I think they changed that because some rifles "required" feed ramps with the lower angle, since rounds would hit the bottom edge of the chamber on some. The fitting block on the front of either piece requires some persuasion to create somewhat of a hook instead of being flat, to engage the tab on the receiver without slipping, they could probably either machine the tabs to be thicker, or include a slight angle from the machine shop. I've seen people use shims to achieve the same result, though that only complicates things.