I'm considering picking up Redshift for Houdini.

Does it have any important limitations when compared to Mantra? I know it might not be the best for very complex scenes, but other than that? Are there any kinds of geometry / volumes / etc that simply don't work with Redshift?

I've played around with demo version and from what I can tell everything works great, so what I'm looking for is mostly - are there any hidden traps I should be aware of before going for full license?

I think out of all the 3rd party renderers, Redshift is one of the best. I know there are some workarounds needed for some of the whitewater and fluid simulations, but for the most part the developers are pretty responsive to user requests and if there is a way to figure something out, they do.

One of my biggest gripes is the lack of some sort of shader ball option, and trying to get your RS textures to display properly in the viewport can be a substantial hassle.

Another concern could be that Maxon just bought Redshift. I don't know what that means for future development on competing platforms like Houdini. Some say it's a non-issue, and some like me are far too familiar with past history not to be a bit concerned.

My advice would be to read the various posts in the Redshift forums, particularly as they relate to Houdini. That should give you a pretty good overview of what you're getting yourself into.