I think that it's kind of a toss-up, and whether the pros outweigh the cons will depend on the type of business being conducted.

On the one hand, they do seem to feel compelled to spread the word. If they are likely to spend a large amount of one-on-one time with customers or co-workers, this could be a problem.

On the other hand, they don't celebrate holidays! If you want to stay open on these days, with minimal haggling amongst your staff, you might consider adding a JW or two.

They will preach until the cows come home, it is in their programming and that's some intense programming. I grew up as a JW and I once hired a JW framing crew, I could not wait for the project to be framed out so I could get them the hell off my job site, I didn't even call them back for deficiencies.