No it's not paid, it's with a fee as usual.
https://grinpro.io/Running it on my Vega64, 3.1-3.2 G/s, best speed so far on AMD cards.
That said, for NVDIA chipsets, GMiner 1.22 is out as of yesterday, giving similar speeds with the latest version of bminer, 1080ti=6.2 G/s
Also it does
not require Cuda 9.2 or higher

Yeah Grin definitely prefers Nvidia cards, I believe it's something with the route the card takes to communicate, Nvidia cards are able to process directly and the AMD has to talk to the CPU first or something along those lines.