licenses for compressor

Does anyone know if I wanted to buy compressor how many devices I could download it on? If more than one can multiple people use it at once?

I read somewhere there are commercial licenses for compressor. How would I be able to differentiate which license I want to buy? How many users can be on the commercial license? Does it cost more than the original $50 to do commercial?

Sorry for the crazy amount of questions that just happened above. Would appreciate any info on this though.

Thanks for you help,

T