Roon Essentials has no signal path, no DSD, no streaming to Meridian, Squeezebox, HQPlayer, the high res PCM audio is capped at 192khz, it has no private zones, it has a 15k track limit (for this box, other boxes will have different limits), there are no composer/work pages, no Roon Bridge support, other stuff.
Technical support for Roon Essentials is done by the vendor, and not by Roon Labs.
It was a last minute decision to give our Roon Ready partners as much support as possible, so Roon Ready devices will work, as will Airplay.
They are on http://roonessentials.com instead.
There is no upgrade path to full Roon.