Review invitations can be sent on basic plan. Only 100, though, but you can choose internally which customers to invite. I don't see that as a problem, because people do need to be reminded (or asked) to write positive reviews, because when everything is working as customers expect, many won't be bothered to venture onto review sites to write about that. So they must be asked while hot. And it's much better than offer any incentives to reviews - many companies aren't shy to do exactly that, but that's where the line gets crossed..