Valkyrie Summon x10 -- totally worth it
Had 120 ancients saved over past 3 weeks -- got her on my 3rd set of 10 ancient shards:
Total from 30: 2 legendaries (Astralith booo, Valkyrie), 5 epics -- very good luck
Having already got Martyr, I did some initial arena and CB comparison with identical gear:
1. Martyr hits harder and her hits have more PvE utility (decreased def, decrease attack)
2. Valkyrie shield is a monster (it's like a 40-50% HP shield on my attackers every 3 turns - superior to Miscreated Monster shield ability and 30% HP shield set)
3. Booking Valkyrie is a nightmare (13 books) and -1 turn CD on A2 comes at end of these books
4. Between her and Martyr, my CB fight went from 6min to 10min+
5. Gearing both is easy
6. Valkyrie arena TM manipulation in theory is very strong, but not significantly noticeable
Summary: there is way worse legendaries you can pull. Valkyrie is definitely good, and even if you are waiting for 2x summon chance, you should try for her. Ancient shards are not that hard to get, void i would save.