I bash a Muggy and I'm very happy with it. IMO a 1515 is better suited to bashing, but if you already have the 1521 you can make do (hopefully it's length and weight doesn't cause any issues). I have only jumped it a few times and I suck at it, and it still holds up to my abuse. The stock control arms are a bit weak, but with RPM LST arms and their LST2/Muggy conversion kit they're much tougher (though I'd recommend replacing their turnbuckles with Lunsford 4x36mm turnbuckles, I sheared a stock one in ~2 minutes). Overall I'm VERY happy with it, I am 100% happy with my choice to sell my Revo and get the Muggy.
Here's a quick video I had taken of mine:
http://www.youtube.com/watch?v=occUrFLw58U
My biggest problem with the Muggy so far is it needs a hefty servo to move those beastly tires around. My Hitec 985MG had no issues steering my Revo but it struggled with the Muggy. I put a JR DS8711 in there and cleared everything up.