If u are still struggeling on HBM3 and on insane dungeons, mechtessa isnt worth upgrading. She needs 10/10 skill and devo to shine. Once u get here there put high revit on her and buff her speed up with micha. Her procc get crazy.
Depends on what you are doing now.
I wouldn't stop leveling an Anubis or GS for Mechtessa. However, if it was between her or Immortep, I'd go with Mechtessa.
She's not a bad hero (none of the newer heroes are bad), but she definitely doesn't have a critical niche at the moment.
That's a fantastic talent for her. I think you'll find her a very good hero. But, like others above have said, she's not a priority at all. Even with a great talent. Aries, Anubis, GS, Grim, Val, Cupid, PD, Mike, Ronin, SK, DD ... there is a long list of heroes to develop and get to at least 9/10 before working on Mechtessa.
I maxed mine out because she looked fun and I had nothing else to do at the time. And I like her. She's legitimately fun to play, which is more than I can say for some heroes. Just not a priority.