I use ChatterUI (available on Github) because I found it faster and smoother than the rest of the clients available for Android.

Yes, the gguf models on Huggingface are totally safe. They will run locally in your phone. You don't need Internet connection to run that model. So, it is safe. No data will ever leave your device.

Edit: There is only one client available on f-droid: Maid But it never worked in my device, unfortunately.