This is a slot machine game. All I can recommend is to stop refreshing - stop pulling the one armed bandit - and save those crystals to buy known quantities of gear in the store.
Gear showing up is random, but within 4-5 days mostly reliable, and you know what you're crystals will get you.
The raid is the raid. I got a full stun cuff once... but after SO SO many raids it felt more like getting a dry bone then a reward, not worthy of mention. Maybe if we could hope to get one a month, every two months, from raids it'd be something to write home about. but 1... 1 full cuff since we started doing raids.
What's really bad is there's probably people who have never gotten a full stun cuff...