It’s part-of/included with the TV Guide Subscription
https://www.tablotv.com/products/tablo-dual-hdmi-ota-dvr/
However, Tablo DUAL HDMI also offers the flexibility to stream live and recorded TV to additional televisions within the home via select streaming devices and smart TVs with an active TV Guide Data Service subscription.
Right there on the product page. Although it’s not as clear in the blog announcement…
(I can’t say with certainty that point was always clearly made, but was easily found early on)