Purified Orb

Is it better to spend my shards whenever I reach 30? Or save up a larger amount of shards?

I currently have opened 2 and I bought two orbs some hours ago. I tend to cover the orb when I go to purchase because seeing the quantity bothers me. I try not to look at my shards left back either, but I usually end up looking at the tiny bar on top to see how many more I need until I can buy another orb.