Free of charge to read (is there a catch ?).
I wouldn’t say there is a catch to the FreeBSD Journal, it is done as a free service by the FreeBSD Foundation as a way to help advance FreeBSD awareness and a way to help keep people up-to date with what is going on in FreeBSD world.
While the FreeBSD Journal is now offered for free (this happened early last year) if you do like it, please consider donating to the FreeBSD Foundation which will help the foundation out in many ways.
For more general BSD news there is also BSD Magazine which offers free issues as well as paid subscriptions that includes more issues and workshops and tutorials.