I've been planning to buy Beersmith before my next brew day. Once you have a product key, can you use that key on multiple devices. i.e., I've got my desktop computer that I do most of my work on. But I've also got an old laptop I've been thinking about formatting to Ubuntu and using as a brew day computer, and then the mobile app for brew days at a friends house, etc.
You can use the product key on the laptop but would need to purchase the mobile version for tablet or phone. I have both and prefer Beersmith over Brewers Friend.