I have a bunch of real world experience with Ab Initio. It is the overpowered Cadillac of ETL tools.
I highly recommend it if you have gigantic amounts of data and lots of hardware to use it on. The terabyte and up problem class. Usually, data is measured in terabytes per hour and dealing with picobyte data sets is not uncommon in an ab initio setup.
If you are not dealing with that much data, I do not recommend it. Ab Initio is geared for the massive data set and if you don't have that much data it'd be like shooting a fly with a bazooka. Yes, it gets the job done, but the cost of lugging around the bazooka instead of, say, a fly swatter, doesn't justify its use.
Lemme know if you want to know anything else!