If you don't have the means to get her to 3 stars, I would advise against it. And even then, she isn't as useful as she could be, as she clashes with the current meta. She will be more useful with the inception of the Kage treasures, whenever that is.

The main reason she is extremely strong in the Chinese version (I thought it was the HK version?) is because there, GNW Tenten has no battlefield cooldown, meaning that it is possible for you to execute her move on the first turn, if you have the ninja to get you chakra.
For us, she's not as useful. During round 2, it's more important to get out fast mysteries to interrupt your opponent, so you use chakra. Getting 60 chakra on top of that is hard.

She's a neat ninja, but for now, at least, she's going to be on the backburner.

That said, I got her 2 stars, just because I wanna be a ninja-mon master. I gotta catch 'em all, at least as much a f2p can get

This isn't exactly true.

With Sage Naruto, or even Sage Jiraiya, you will want to pull of that Rasenshuriken/Toad Oil before your opponent in order to interrupt/cc/whatever. Like I said above, after that 40 chakra has been consumed, it's nigh impossible to get back 60 chakra in order to pull off her mystery in that time.

After round 2, her Critical Hit buff expires and your mystery will do significantly less damage.

GNW Tenten's main appeal was the ability to use her mystery in conjunction with her Critical Hit buff, but that doesn't seem to be an option. Her main use right now, in my opinion, is to paralyze your opponent every round with her chase, but that isn't super useful, unless you're faster than them. And if you're faster than them, you could probably beat them without GNW Tenten.

Don't get me wrong, her mystery still hits hard, but it's nowhere near as strong as it was hyped up to be.

Oh, you're right, I forgot about Chikamatsu Chiyo!

Yeah, GNW Tenten works with Chiyo, I'd say. Being able to get up to 100 chakra every round is pretty awesome