It might be kinda expensive but that 9 x 10 summon that grant you extra 600 shards is kinda a late game investment , even if you didn't have the unit itself as shards capped at 600.
If we also consider the cost of normal 10x summon without guaranteed banner:
50 x 600 = 30000 visiore
9 x 2000 = 18000 visiore
total = 48000 visiore
I did the first for the 3 rainbow orbs, didn't realize it said 300 shards at first... already had ayaka TMR, if I had gotten her again I could trade for two UR tix, but got rain shards, got sakura, saving the last 6k for future banners