The Spiral Kiiutan might be better than Jaan, but I only play Tohaa (I think they're significantly better and Taqeul are my favourite unit), the Kiiutan profile in Tohaa is rather underwhelming. They do not prevent re-entering impersonation.
No, you cannot be in marker state when you assign the mate (Assignable rule). The Hatail Spec Ops blister is a Taqeul, I'm pretty sure it got renamed before release because Tohaa got discontinued, because the model looks nothing like a Hatail (it's modeled with SymbiontArmor and Hatail Spec Ops don't have them). It also has a outstretched pheroware-looking arm.
Can't start in impersonation but can reimporsonate I believe. Kiiutan is pretty great in some matchups, but Jaan is pretty great in all matchups. I think it's perfectly reasonable to bring one list with a Kiiutan (maybe a list specced to fight CA for example), and your main with Jaan. (I'm a Spiral player who doesn't play Tohaa btw.)