when mental ray is setup like it should you will have faster rendertimes.
even scenes with a very high number of polygons will go very fast (read : 'fast enough to be productive for your clients')
when the settings are to high you will have exponentially longer rendertimes.
so you could say the 'room for error' is a lot smaller then with other renderers.
this might be the reason why people keep talking about the 'steep learning curve or mental ray'...
always try to limit the rendertime in test fase, obvious things like :
- render in smaller resolution, render in regions, ...
- when using stuff like depth of field in Mray, you will need very long rendertimes. setup the sceen without those extra's and then turn them on when all the others parts in your scene are setup fine.
- ...
exterior is a lot harder to master then interior in imexp.
cause the mray in max has only ONE photon bounce. there are some way's around this, but i feel this feature should be solved in the next release of max/MR.
so in anwser of your question : YES Mray is worth learning, but it will take you longer than other renderers probably. but onces you got the hang of it, you will love it
