Well, my father has one and I've shot it. Recoils about the same as a Garand, but the sights aren't anywhere near as good. WAY too many small parts in the gun. Making one would be expensive. While the M1 wasn't an easy to manufacture gun, the Johnson would have taken even more time.
One cool feature was the quick-change barrel. You flip a lever under the barrel, and it comes right out. Makes cleaning and barrel replacement pretty easy. Theoretically you could have several calibers of barrels made for the one rifle and switch between say .30-06, .308, .243, 8mm, etc. in seconds.
It used a rotary mag. The mag is loaded by single rounds or 5rd Springfield stripper clips. Two clips loads the mag. You can load the mag while the bolt is shut, so you can "top off" anytime you want and still shoot. The mag itself is thin stamped metal, and it sticks out all around the bottom of the rifle. It's pretty easy to see that it would get dented easily in combat and that would definately effect function.
The trigger pull is VERY long. I mean it was a strange gun to shoot. The one I shot was a .30-06 weapon that was one of a batch made for the US military, but I don't know the serial number etc. It could quite possibly be a B.S. story told to my dad when he bought it. One of these days I'll have to research it and find out. It's definately not a sporter, and not a Dutch gun. I haven't seen it in years, as they live a couple thousand miles from me. It was a fun gun to shoot though.
I've handled the LMG, though never shot it. It fired from a closed bolt on semi and an open bolt on full auto. The rifle is closed bolt only.
They are in the over $2K area now. Top dollar for ones that are in GI trim. The sporters are towards the low end of the price region. The gun is a rare collector piece now, but the gun itself isn't worth that kinda price. I'd expect the price to do nothing but climb in the future.
Ross