Grailing Hans?

Yes.
He'll benefit from the extra HP to stay alive.

Ideally, you want to grail him to level 80.

There are ways of getting around the low stats such as Volumen Hydragyrum, Chaldea Lifesavers etc. I would save the grails for a DPS servant. In general, grail servants you like and use often.

I wouldn't. With a good team he can stay in the field for a good time without spending your grails. In the end is your desicion tho, your chaldea, your style.

Is about 525 HP/grail worth it? I don't think so, since grails are extremely limited. And I say that even though Hans was glued to my frontline all the way through Babylon. I was lucky enough to have a Volumen Hydragyrum though. Without that, I'd probably go for a CE that would guarantee a T1 or 2 NP, or maybe Arts up.

If you have enough for any future husbandos and waifus you plan to get and plan to use hans long term then yeah id say it is, makes life a bit easier with him dying less, up to you really

I have him 10/10/10. Put on 2030 CE and he will work without grails.

He works fine without grails. One day, you might even get a better support like Waver for example and he'll somewhat retire as your Employee of the Month Support.

As usual grail for love. But game play wise, Grailing DPS servants is better since: Additional Attack for DPS > Additional HP just for Survival. Unless that servant is Big Sis Jeanne.

If he's your favorite servant, then go for it.

Grail him if you love him and plan on using him even if you get Merlin/Waver. If it's just for gameplay, stick a helpful CE on him (I personally use Demonic Bodhisattva for shorter fights and Chaldea Lifesavers for longer ones).

Circa. Camelot he does become very squishy, especially when Innocent Monster is up. But for the most part, by the time he dies, he's already buffed/healed his teammates enough that they'll finish the job.