I have a number of books that talk about "the science of cooking," and one of them is about spices. It has a section that talks about "meat rubs and sauces." It's actually very easy to make your own – there are only a few "key" ingredients.
I don't like to use commercial products anymore, because of three things: too much salt, too much sugar, and MSG (often disguised as "hydrolized yeast extract" or "celery extract"). I have a food allergy to the latter, so this is very important to me.
Before you buy it, read the label carefully. It's kind of disturbing to read the ingredients list of that appealing-looking box or jar on the shelf. (If the name has more than three syllables or sounds like it came from a chemistry lab, you probably don't want to eat it ...) If you make your own mix, you know and can control exactly what's in it. (You also learn simple tricks such as lightly grinding the spices with a mortar and pestle before adding them, to release their flavors.)