Crafted this a few days ago and enchanted it with executioner and overall it's very badass both in looks and its fuction.  All comments about the weapon proc on this are true, it's pretty rare and most stuns come from the warrior talent tree.  It has proc'd off of all special ablities (not shouts or stomps of course) but I've had it proc off of <slam> (answering question above) and even <rend>.  Spamming hamstring does increase the chance of a stun but again mostly talent one.  Big MS crits, but I would suggest gathering up as much + to crit as you can (coming from being axe spec the loss of 5% ment I needed to make up for some of it) to maintain a good 30%.  Personally, I noticed white damage being more on the top end and when it hit big it hit BIG so definately worth switching proffessions and spec for. 

I hope any of this helps anyone reading up on this weapon.