While XSL-FO processor are being developed, you have to consider how complex your formatting requirements are and how well any processor meets your need. FOP certainly does not all the features you'll find in the Antenna House product but probably does most of what you want for a basic magazine layout.
As for the complexity of FO, it certainly covers a broad spectrum of formatting needs, but the basics are not so difficult to pick up with a little practice. If you have a fair working knowledge of XSL and any experience with CSS, you should pick up FO basics easily. I've picked up what I know by just Googling and reading and building from simple to complex.
