Procs aren't reliable as a means of debuffing though. Nice toys, but while you're wielding the Journeyman's Walking Stick or Willsapper hoping for a proc, you're not doing your normal dps. Plus, Willsapper is only 35% slow, and will typically be mitigated, is it really worth the time taken to make it proc?
As my ranger, before I got both epic 1.0s, I had a Swarmcaller (procced Tagar's Insects, up to 50% slow, but probably around 45% the levels I used it), and would sometimes take most of a fight to slow a mob, which meant it took longer to kill and did me more damage than it would if I'd just gone with my dps weapons from the start. Of course, there were the times it would proc first swing, but it was probably break even whether it helped or not overall.
I would find there were some fights that if it didn't proc soon, then I'd need to heal before the mob was dead, whereas if I used the dps weapons, the mobs would typically be easily dead before I'd heal, simply because I was outputting the dps. At that point, it became not worth using. Fortunately for me, I got Earthcaller at about that time.