Yeah it's pretty nifty, they seem seriously motivated in making it a full alternative to 3delight.

I can understand someone who already uses both Poser and DS might want to try it but what are the other options open to Poser users that only use Poser and don't want to go down the Daz route?

Good news is that there is more choice in renderers these days then ever before. There's VRay, Arnold, Redshift, Octane, Thea, Indigo, moskito, Maxwell, Cycles off the top of my head as well as various old workhorses like mentalray, finalRender, PRMan, 3delight, Vue...

The bad news is that only a few of them offer any kind of serious support for Poser or are affordable. There's lux of course which is free and has good support via Reality but is painfully slow. There's Octane which is faster but isn't exactly cheap. Also good old C4D + interposer but that's even more expensive... Compared to those, iRay does seem like a 'best of all worlds' renderer IMO.