The pricing breaks down as follows: The first line on T-Mobile Essentials costs $60 per month, while the second costs $30. Each line after that, for a total of up to six lines, costs $15 per month. But if you don't have autopay set up, that will cost you $5 more per line.
The release also contains this nugget: "Without autopay, it's $5 more per line. During times and places with heavy network demand, Essentials customers may notice slower speeds than other customers." Basically, this means that customers on the Essentials plan will be the first of T-Mobile's unlimited customers to have their data throttled. The fine print goes on to say, "During congestion, Essentials customers may notice speeds lower than other customers and further reduction if using >50GB/month."
T-Mobile's unlimited plans are a bit confusing: there's now Essentials, ONE and ONE PLUS. If you don't use a lot of data, but want an unlimited family plan, Essentials sounds like a good deal. The plan will be available in T-Mobile stores starting August 10th.