Pros
There are lots of opportunities for accruing B2B writing and editing experience, depending on the owner's whimsy; that is to say, he'll sell the job to you in the interview stage as "writing-intensive," but on the job give you work that doesn't require any writing, only research and "re-writing." If you _are_ given the opportunity to do some writing, however, you'll probably actually get to see your name in print, which is a plus. In short, it's an okay opportunity if you're fresh out of college, or in college looking for part-time work -- that is, however, if you're willing to tolerate the job's cons, listed below.
Cons
This company is a mess. I was hired and fired in less than two months. I did some research and it looks like the longest duration anyone has spent in the Editorial Assistant position is less than six months, which gives you an idea of how inhospitable the work environment is. The owner yells and curses every day. I literally heard him say "F*** you" to one of the sales guys on a regular basis. He yells at you when you do what he doesn't want, but equivocates when explaining what he does want. I have a suspicion that he actually enjoys firing people. Like the other poster said, he knows what he's doing in that he's been successfully serving the landscape and irrigation niche for a while, but the guy is sadistic, frankly. Oh, and never disagree with the owner. I witnessed someone get fired for that.