*speaking as your waifu-loving-brother-in-arms here*
Well, I assume you're keen on sticking to FKG-X... which means no plans of looking at the gacha on .com ever? Anyway, whatever you get should be retained in your knight roster [data], regardless. If that were not the case, it would piss off completionists like Allocer, etc. Whether you roll the gacha or not, that's all up to you.
At the very least though, there's still a very good reason to pop into .com/iOS/Google Play app: clearing/farming collab event stages for rewards. Like in poll events, accumulating 10k collab currency will give pretty much everything (beyond that, it's just extra 5k coins/step).
That said, I also don't intend to roll TenSura gacha (it doesn't interest me that much), even though I've been playing in all-age for the longest time. To be honest, I hadn't even heard of the anime until it was hinted in the last stream. NGL though, Treyni looks nice. Shion, too.
They actually have date scenes (unlocked at 100% affection) which, like the story scenes, are limited and will disappear after the collab. (Added to first post on my thread.)