Coins are the usual complaint. Ryne publishes no conversion between coins and words, so 10,000 of them is a number without a unit and you cannot tell whether a 3,000-word chapter fits until you spend some finding out.
The 750-word request cap at $29.99 is the other. That is the highest entry price on this page paired with one of the tighter per-request limits, and reaching a 1,500-word cap means moving up to $39.99.
None of that makes Ryne a bad tool. It makes it a tool with a shape, and the question is whether that shape matches your work. Our full HumanFlow vs Ryne comparison sets its numbers against ours in detail, including where Ryne wins.