-You have a free draw per day.
-Special Item named "The Key of Equip. Chest" can be used instead of diamonds.
-When you have 10 keys you can do a x10 Draw.
-x1 Draw cost 80 Diamonds.
-x10 Draw cost 680 Diamonds if you're not using Keys.
-Everytime you open a chest you get a special "shard", when you open 10 chest you get 10.
-"Shard" can be exchanged with alloy or Awaken Weapon.
When you do a x10 Draw you will get an Awaken alloys a Legendary item (cf equipment guide).
Rewards there can be very good if you're lucky like Digivice or Rings, I don't recommend to buy x10 draw with your diamonds and use only you're key.
I also recommend to use you're key when big event are happening that's need to open Equipment chest.
I also recommend to wait something better to exchange the shard since those have a big value and beside the Greymon weapon nothing is good (But I still don't recommend to use them on the Greymon weapon)
Here is an example of why you should keep your key, by keeping them that allow you to get an Awaken Weapon for free (or almost) those event are worthy but don't waste your key if this one is not so good (for example when you don't use the digimon).