What does this link show you?:
https://play.google.com/store/apps/details?id=com.plunien.poloniex&hl=enI can access the above link just fine, which means they didn't remove the app from the app store but it's possible that they are restricting the app from certain locations, and that's why you cannot find it by searching for it.
As to whether you should be using the exchange then it's up to you but I personally would feel more comfortable using something more reputable such as OKX, or Bybit.
If i am accesing that link i see "We're sorry, the requested URL was not found on this server."
The problem is i have some funds there already, enough to worth fighting for, contacting a laweyer or find more people that had funds frozen by them and act togheter, i am from a 3d world country and it worth to fight hard for me.
i tryed to acces the link from a laptop and 2 phones and i have same problem