Xaku is one of my basically never used frames: I use Zephyr for box breaking, and now Caliban’s kit has a lot of convergence with Xaku. Honestly the most exciting thing about Xaku for me is the weapons that came with their release… although I’m kind of sad they passed over the Sepulcrum for the shiny prime buffs.
One nice thing I can say about Xaku is that they’ve aged magnificently. Essentially the gold standard for a high performance all-rounder. If you want a chill tank, Vampiric Grasp is great on health conversion tanks, and it might even be possible to get a functioning energy tank going, although the mod requirements for such a build might not fit. I’ll experiment once Xaku Prime is out of the oven.
The worst thing I can say about Xaku is they feel like they’re in the wrong game sometimes. Having six abilities sounds great, but the “ability wheel” style abilities always feel too slow for Warframe for me.
One very specific niche Xaku enjoys is as the best Syndicate mission runner, as combined Golden Instinct and Vast Untime make it very easy to quickly locate medallions while you’re getting a feel for where they can be for a given tileset.