is st teresa's tiara worth it?

[Master-Steel]

I bought it from a bazaar for 10k. was that a mistake? im not really sure who i should be using it on lol

[Midas Gloves]

If you put it on a group that doesn't use their Magic stats at all it just allows you to go all-in on STR+SKL. If you have a group of Archers or pure melee for example, that's a pretty big boost to those two stats across all units.

[Horthas]

It's very good. Personally I often used it with Diana. It makes her squads healing a lot weaker, but she's easy to push up to massive strength. It's also usable in squads that might not need healers (greatbows, horsebows on the hit and run). It also seems to stack with Arcane Might which I wondered about. It doesn't stack well with the other unique strength item, Fangs of Duros.

[Grand Historian]

I have Jules with an all warbow squad and it works great

[Master-Steel]

nice thanks for the tips i think ill give it to jules then with his archer squad

[Horthas]

Another couple mentions. It goes really well with Soha's Blood artifact since that can get you healing for damage. And it turns Valkyries into strangely hard hitting units potentially. I'm not sure how much value that has. They still don't attack twice (I think?).

[Ballistic Groove Gun]

Valkyries (and paladins) only swap out their second attack for a heal if there's any units below 50% hp. On the other hand, everyone that can heal will heal even if only one or two heals are required to fix things.
But yes, blood shard pairs nicely with the tiara since it doubles up on the str boost (I think) and also counts as a source of healing, paving the way for stuffing more hard and multi-target like centurions and knights and zweihanders and stuff into the formation. Rogues and rangers love it too since they reach where regular melee doesn't and can benefit pretty well from stacking even more skill.