Everyone should learn some music theory, even if you only play a little as a hobby. It will improve your playing and understanding of what you are playing. I bought their bundle of Circle of Fifths, Chord Compass and Cheat Sheets. I used to play bass in bands long ago, and have been meaning to get back into it. I had a decent understanding of theory and the circle. But, out of site, out of mind, I wanted something to get me back where I was in that area, and possibly take me further.
These tools are extremely useful, They are built well, so are sturdy. They are designed well, allowing for an interactive experience for learning and using music theory.
Music is a multiple skill endeavor, physical and mental. I knew a lot of musician's that had the physical aspects, the mental was mostly knowing some chords and their names, and some fretboard notes memory. As good as they had gotten with that, once they started to learn even basic music theory, their playing improved exponentially. It may seem daunting to some, but it's really not. Like anything else, small steps, (No one learned higher level math without first learning addition and subtraction, then division and multiplication) These tools help with those steps. (The music, not the math ;) Though math is a factor in music, it's not the primary means for learning theory :)
It's not just the tools they provide with your purchase, they also include instructional books for understanding the theory and using the tools. I would probably only change one thing, in lieu of the current great packaging, I would prefer they were in a clear heavy-duty plastic envelope, to store the booklet and tool in. (They are sealed in a heavy plastic wrapper. which saved me from a poor delivery person who left them outside on the floor when it was raining, instead of a delivery box I have outside. Thankfully these are in a well sealed plastic packaging). If the packaging was using a reusable plastic envelope, they could still be sealed in thinner plastic to protect from moisture damage in shipping. But that's not a deal breaker, just a suggestion. The product is worth it either way.
If you play guitar or bass, you should get these. (They have piano products also, so I assume they are just as good. I'll find out when I start messing with piano. For now, I can only speak to the products I purchased. ;)