I have seen this question asked several times over a few months. I myself have asked this question with little answers. So Here is my solution and response to someone who asked this a few days ago. Thought some might be interested. Enjoy.
You have to modify the locking plate for it to work. If you are using Colt or NHMTG mags you need to dremel the locking plate for the ranger plate down to fit past the GI mag locking floor plate tab. Remember you will only be able to put 18 or 19 rounds in to seat the mag on a closed bolt after this modification. Also the floor plate lips are a little larger on the 20 so sliding the ranger plate on will take a little work. Remember to use a small tool to push the floor plate tab in to slide the ranger plate on, ( tuff but will work).
I personally have not shot very many rounds out of this yet so I don't know if it is fully reliable. It apears to be working 100% at this time for me.
Here is how I did it with steps and pics.
Glock armoer tool, Dremel, and razor to score the cut on Ranger floor plate.
Step #1
Score the ranger floor plate with razor on both sides and snap off. Remember to line up plate with mag bottom to approximate location for brake just at or past the mag locking tab..
Step #2
Dremel down the locking floor plate to fit behind the mag locking tab. A little at a time making sure it wont touch the locking tab. I had to go past it a little to make it work allowing room to place it in and remove it.
Step #3
Place ranger locking plate in mag. Turn it to the side as the tabs on the 20's are larger and it may take some work to get it in.
Step #4
Sliding on the ranger plate. This takes some minor elbow grease. As the mag tabs are larger you will have to work it on. Once you reach the locking Tab use a tool to push it down in to the mag slightly so the ranger plate will pass over it. I used my Glock tool.
Step #5
Slide the ranger plate the rest of the way on and check that the ranger locking plate has locked on to the ranger plate.
Step #6
Now your done. As I said before Im not sure on the reliability at this time. Function test it and run rounds threw it to confirm it is working and enjoy.