The Toys include three crystals to start and packs of three different crystals can be purchased to obtain the other type crystals. The big draw the toys offer is the ability to light up in response to your use of Z-moves in the game. The bracelet actually responds to the sound of your 3DS as you use an in-game Z-move and lights up based on the sound. It is a really interesting immersive feature but is a little costly at around $30 USD for the bracelet itself and roughly $5 USD for each pack of three crystals.
Source: Nintendo Everything