Different products entirely. Roon ROCK is software that can run on the Roon Nucleus, a small, silent computer for running Roon core (ROCK is a version of Roon core). I understand it also can have output to your DAC, so if it’s in the same room as your audio system, you won’t need another stream receiver (renderer).
The Aries G1 is a stream renderer. It works with Roon, among other protocols, but to use Roon, you’d also need a computer of some kind running Roon core. You could think of the Aries as an Ethernet-in, USB-out adapter (though
No matter what you choose, if you want Roon, you will have to pay for the software part of it, too. Last time I looked, that was either about $120 per year or $700 per lifetime (yours or theirs). The Roon subscription is NOT included in the price of the Nucleus. (ROCK itself is free.)