Later on, focus banners are even better. Like this one currently featured in tw.
It has 2 benefits.
1) The first SSR I pull in this banner will be the one I don't have.
2) If I pulled a char that I already have, and the char I have is 6*, I will be given an exclusive item to trade the shards I got for the pull for the shards of a char that I don't have.
Eg.
Let's say I already have 6* Luna but not Tiaris or Clarett (also known as Little Cherie, Cherie's descendant in Langrisser 5)
1st SSR pull I got Tiaris.
Assuming I decided to continue pulling, 2nd SSR pull I got Luna. But since my Luna is already 6*, I have the option to trade 50 Luna shards to either 50 Tiaris shards or 50 Clarett shards (I choose this of course).
If I pull Luna in my 3rd SSR pull, 100 clarett shards will make me able to unlock Clarett.
If any of the 2nd/3rd pull is Tiaris, RIP...
This is not as good as the couple banner event, where u can unlock the SSR u don't have by pulling just 1 dupe (That event trades for 60 shards instead of 50 and do not have the 6* requirement), but still offers some protection against dupes.
Concluding advise:
This game has no powercreep. New chars released do not powercreep over old chars. Day 1 chars like Leon still remains the top chars in pve. New chars mainly adds flavour in pve or is pvp inclined.
There is no hurry to get ssrs as u can see, day 1 ssr like Luna and Tiaris are still featured in focus banners in tw, which had been released for more than 1 yr.