My friend has a midget RR male that is about 50lbs and his frame is smaller than my 50lb GSD/Sibe mix girl, so he's got much heavier bone than her. They have about the same energy/drive actually.
He can go all day, but he does have an off switch unlike Mali's.
I'm talking hardcore running + frisbee or whatnot.
And you'd better keep him on leash because he is a hound...
Be prepared to have a lapdog. I had him laying along my torso with his head on my shoulder and his big bro under my legs while I was reading on the couch once. Its so totally irresistable.
They are stubborn as *explitive deleted*.
He does not like other dogs all that much, but can live with them. He got along really well surprisingly with her daughter's RR/Lab mix boy. He currently lives with a pug and tolerates that nasty little dog trying to hump him (the pug needs lose his nuggets very badly....).
They will protect without even being trained for it. I've put basic OB training on this boy, but he's had nothing else besides that. Last summer I had to exercise him at night to avoid loose dogs while I was babysitting the RR boys. Some creeper tried to sneak up on us while the dog and I were playing tetherball... um lets just say he did a perfect untrained bark and hold, then returned to me on command.
I would LOVE to do Schutzhund with a RR. But they are very much not for everyone in a lot of the same ways Malinois are.