the major differences I've seen are how they are made, the number of DIN threads and how compact they are.
Some of them come with 5 DIN threads and some come with 7 DIN threads. Obvisousely the 7 DIN threads are a little stronger and don't leave 2 exposed threads on your regulator. However, the 5 thread ones are still plenty strong enough to exceed the pressure rating of the yoke regardless.
APEKS makes a very nice 7 thread one. I actually bought the 7 thread Dive Rite one because it was about half the price, however, I've seen some Dive Rite ones that are 5 threads and some that are 7 threads.
I also noticed that some of the brands are exactly the same but just with someone elses logo on them.
Another small minor difference is that some come with the yoke dust caps and some don't. Typically this isn't an issue as you would use your DIN dust cap on your regulator. However, if you were on a liveaboard trip where you used the same yoke k-valve tank all week long,you typically would remove the regulator for the crew to refill the tank. Most people would like to have a dust cap on their regulator for the time period it was removed. (some it might not matter to...). But this isn't a big deal. You can buy replacement dust caps typically for under $5 bucks and put on your adapter.