Use it everyday, very powerful and useful, can automate all kinds of functions. I have Rules that delete VPS files, send out email notices, Move files, build jobs from hot folder dropped files, etc. Major time savers and standard work improvements. That's the PRO.
The CON is very hard to learn, the learning curve is very hard. Simple Rules are easy to build but quickly get hard as you get more complex. It takes A LOT of time and effort to use it.
BUT, once you get it going, WOW!