There are only two features that seem quirky compared to qbrew. First one, when I input hops I think it should default to "oz" without having to type it in or click the "edit selected" button. If you type in "1" in the amount it defaults to 1lb of hops! (not that I don't love a good IIPA). Qbrew has little arrows next to the ingredient amount to easily scale from .5oz to .75 to 1.0, etc....that would be nice.
One of the major points of brewtarget is that you can enter amounts in whatever units you please. You shouldn't just type "1" in for the amount of something, but rather "1 oz" or "30 g" or whatever. It will automatically get converted to the appropriate units based on your unit system in the options.