I've tried LANDR (free) on 2 mixes. I chose the highest level of mastering. Here are the + and the - :
+
After reading some posts here, I was expecting an awful result. It's not the case. I don't feel betrayed, my work remains my work...
I think that LANDR cut some bass frequencies and it was right. My mix was too bass-heavy. The final result is good.
-
LANDR maybe added too much brilliance to the sound. Maybe just a question of taste. And that can be fixed we further equalization.
It was difficult to achieve the process, because the server sometimes seemed not to respond.
There are not many settings.
There are no advices, except when your file has not a big headroom, it is refused. That's what I would actually expect: after uploading, LANDR would tell me the potential problems and then I could master or return to my mix to improve it before. For example I never know if my mix has enough bass (a good idea for a new SONAR plugin?), I compare with reference tracks and use Analyst but that's not easy.
Big problem for me: I haven't found how to delete my tracks from the server. I don't want them to stay there forever, for security reasons. It's a question of property rights, but maybe I have to search again how to do this.
The pricing / the offer : I'm not convinced. The free low-res MP3 are of decent quality. But we should at least be able to try the high-res WAV quality once on a track, or every time on a part of a track. Otherwise it's difficult to make a decision. And by the way... the "high-res" WAV format is 16 bit / 44,1 kHz. Is it a joke?
You can see that I found more - than +. However I think that LANDR is an interesting addition to SONAR. If the pricing, the resolution and some other things were changed, I may use it and could save much time when mastering. And it is certainly an excellent tool for SONAR Artist / Professional customers and people who don't know anything about mastering. I will wait for improvements to decide whether I want to use it regularly or not.