Dan,
I have heard that the PWNA program sets you up to pass the PWNA Cert Test. They go over the Q's and A's. Don't think you'll come away as an authority on NFPA 96, OSHA and the mechanical code. You'll come away with a gentlemen's knowledge of the subject, enough to discuss it and try it out.
On the other hand, it's practically in your backyard, so for about a grand it's the best you're going to get, short of a full out school. The certification is designed to make you a responsible hood cleaner, so if there is a fire in a place you have serviced their insurance company attorney can sternly look at you in court and say, "And you call yourself certified! You should have known better." As it is now, the same scenario, the attorney will look at you and say."Why aren't you certified. You should have known better."
It boils down to your choice. I'd go for it.