Commercial or non-commercial license [on hold]

I am building some application for computers and mobile phones that will be controlling hardware. The app will be connected to my servers that use Stanford POS Tagger. The app will be free, but the hardware that it is going to control will be paid.

My question is this: what type of license do I need to use on POS tagger on my servers, commercial or non-commercial? I think that I will be good with non-commercial, because the use of POS tagger on my servers will be for my app that will be free. Only additional hardware that can be purchased through shops like retail stores will be paid.

So: APP (free) -> My Servers -> POS Tagger (commercial or non-commercial?) | APP (free) -> Hardware from retail stores bought for some amount of money. But the hardware will not be directly using POS Tagger, it will only do what the FREE app will want it to do.) What's your opinion? Should I use commercial license or I am good with non-commercial?