Yep, we don't charge for seats at all. Just usage. In fact, we're likely going to be adding a lower tier so that individual developers can use the tool (at about $50/month). With the direction we're going with the product, we see ourselves having several "products" long term (error monitoring, session replay, logging, etc..) so there's a lot of value in making smaller teams happy w/ pricing, even as they grow.
And if you ever give us a try, definitely send feedback our way; we have a discord community up at https://highlight.io/community.