A couple people posted about saving your engrams until you are a higher rank to get better gear from Cryptach. There is a few flaws with this, you only have so many slots available, but you could store them in your vault at the tower, until you're a higher rank, fair enough. But the bigger problem with this is, it doesn't work.
Here's gif of me, a level 8 beta, with a Cryptach level of 12, a rare body armor engram
Now saving your engrams to rank up Cryptach is a good idea, because he does give you rewards.
Just don't think that if you wait until you're at level 15 to decode your engrams, Cryptach will only decode your engrams to level 15 or higher gear.