have you done it both arms at same time? how do you think it compares?
Yeah, but not with the kettlebell. I've done them with the EliteFTS torpedoes, heavy dumbbells, dumbbells held by the hex end (for extra grip nastiness), and other assorted stuff. The unilateral ones suck because you're trying not to tilt over to the other side too much but you still want to support this unbalanced weight. More core activation, to use the trendy terms.
The bilateral ones are more work - it's twice the load if you load them evenly. If not, you get a hybrid of the two - say, grab a 60-pound kettlebell in one hand, and a 75-pound dumbbell in the other. Walk around for a trip then switch them. It's a nice variation - you trade a little load in one hand for the thick handled grip work, and for a little off-centered core stabilization work. ANY variation with a long implement (the torpedoes are a good example) is miserable when you try to turn, because the intertia says they don't want to just stop and let you turn them. :)