It's nice that they all seem to be loving, and that it isn't forced for anyone. I did get a feel of "we're having as many kids as we possibly can because religion wants us to" but the kids seem happy so I can't say I find it horrible or anything like that.
I do agree that the main difference with polyamory is how one-way it is. None of the wives are allowed other men in their lives, I definitely couldn't be a sister wife if I knew I wasn't allowed the same treatment. It might work if all the females are mono, but it seems that it's more that they're not given the option, which is a bit sad.
Of course, I can see how they wouldn't have much time for other relationships, they seem busy enough as it is.
All in all, as far as religious polygamy is concerned, I think it's a very positive show. I do think it's different from polyamory though. I also think the law should leave them alone.