Many of the players here will advise you to hold on to those shards until we have 2x boosted summoning rates. It is a good advise. But I say, if you are a new player, like palying like for few days, I suggest you summon. Every day you hold on to those shards you are delaying your progression in the game.
i saved over 1,5 months shards and on double event i used them ....nothing...not even a good epic
last week on queen eva event i opened 15 ancient and 2 sacred shards because of the summon event:
result was unbelievable: queen eva, candraphon, nethril, bad el kazar
this time on valkyrie event i opened 5 shards: hakkon smashlord inside
so thats rng...but all my legis are from not a double event.......but chances are higher to get good epics....for legendaries its minimal from 0,5 to 1 %
I always tell beginners to summon there shards for the first 2 weeks of game play.
The reason why is because as a new player - you lack a lot of hero options.
You really need to bolster up your hero collection.
Save any hero which is Rare - Epic - Legendary
After the first 2 weeks of game play, You will acquire Shaman (7 Day Login) & Jizoh (14 Day Login)
If you haven't pulled any good hero by that time, You can just build up your Shaman & JIzoh.
Than you can begin the process of saving your shards for future events