I got one, nice mag.
There is a trick to it.
Hold the mag upside down, rest your index finger on the edge of the baseplate where you WOULD push it so slip it off.
Then you have to slap the top of the mag against the palm of your hand. If you do it right the baseplate will slip then you can take it off.
Don't put any force on the baseplate with your index finger, seems not to work.
Until you get the trick timing right, you'll end up with a sore palm. However, the other option is to bang it against something else, a lot easier, a carpeted floor should to, try not to bang it on the feed lips.