And it has a really nice scatter plugin, which is basically like an octane cloner. But A LOT faster. Thea is promised to have volumetric support soon as well, but no body knows when yet. Similarly hair support in thea is limited to geometry mode, which will slow down with large numbers, while octane i think has proper hair support. On the downside they have a very closed system. With v3.0 octane will have render farm support, but you'll only be able to use their renderfarm.
No other farms can render out your scenes. So if something happens to their farm you're up shit creek.