I would like to know what is the maximum weight for the smartphone that the new OSMO mobile can handle? I have an iPhone 6 plus with an Otter defender case on and it's pretty heavy.  

You'll have to use it without your case. Here are the dimensions of the opening.
The Osmo Mobile supports smartphones measuring from 58.6mm-84.8mm long and up to 8.4mm thick.

Don't worry about your phone falling out, the locking mechanism is fantastic and after tightening the knob there's no way the phone will slip out.If your phone is curved then you need to be careful as it may not fully sit in the cradle.

DJI-Ken Posted at 2016-9-1 10:21
You'll have to use it without your case. Here are the dimensions of the opening.
The Osmo Mobile sup ...

Thanks Ken for your information. It's a bit of inconvenience to have to remove the case. Otter cases are not known for easy removal.  

Maxi3D Posted at 2016-9-1 22:44
Thanks Ken for your information. It's a bit of inconvenience to have to remove the case. Otter cas ...

I know, I have one on my iPad and I can barely get it off.
I too have a thin rubber case on my Samsung S6 and I have to remove it to fit in the holder.
But I can tell you that if your phone is not curved it fits like a glove when tightened and your phone will not come out.