These are AMAZING accessories!
The toolbelt is great for carrying your brushes as you work, so you don't have to sort through them on a countertop. You can also store small items like wands and sponges and tissues in there, and perhaps a small tube of Duo or Gloss.
The knapsack and briefcase are very similar, the only difference between them is really how you carry them (like a backpack versus like a suitcase). They've got lots of specialized spaces inside of them, like mesh pouches and palette pouches. The palette pouches are removeable, so you can pull them out to tote 15-pan and 6-pan palettes.
The toolbelt retails for $39 in the US, and the knapsack and briefcase are each $150. The toolbelt is definitely worthwhile to own if you like having your brushes on hand... the other two are a much bigger investment that may not be worth it to you. If you have a discount, that might help, but I got my knapsack on eBay for about $80 and that's the only way I could really afford it!