Quote - I am happy with firefly but see that others prefer to use other render engines. Could what those who use reality etc be written into firefly?

I personally use Octane although I also have a Reality 3 license.  Smith Micro would have to purchase the renderer.  Reality uses Lux under the hood which I believe is free/open source and Octane works amongst other tools also like Lux does.  It'd be more limiting for those renderers.

The main benefits to Octane/Reality is that they will use your graphics card to render.  You can render most scenes in under a minute.