Frank AI is one of the most useful tools I work with on a daily basis.
You basically have ChatGPT 4o with many special features. The only thing that I've been missing is the advanced voice chat. So if this is your main reason for using ChatGPT Plus, know that this is not available right now in Frank AI. I do hope we'll get this feature someday.
On the other hand you get many additional goodies.

Whether it's analyzing a medical image or blood samples, extracting text from handwritten notes (impossible with common OCR), summarizing web pages, asking questions about files you upload, generating images - no problem with Frank AI. You can even create your own templates with your own prompts. The special soft keyboard can be used inside many apps like WhatsApp, etc.

A few weeks ago the service was down for almost a week and the app disappeared from the Google Play Store.
However, I think this was due to technical difficulties, because a new iOS version was rolled out during that time and it looked like they tried to fix the issue. Luckily the service is back now. Let's hope, Android users will get it back soon - if you already have the app your Android device, it should still work. If you need to install it anew, you must either wait for the app to return to the Play Store or look for the APK elsewhere.

All in all one of the my most used apps from AppSumo and probably generally.