FaceApp has indeed upped their game with the face swap option. While as noted above, it is not perfect, the neural network technology they use learns and improves over time with the processing of more and more faces.
Two issues I have noted and found reasonably successful workarounds för are:

1) there is a tendency for cumulative edits to whiten the subjects face. This quickly becomes weird and unnatural. You don’t need to even leave the app to fix this, though. Just go to the adjustments panel, select the icon in the upper left corner, select the foreground option, then erase all of your subject except for the head, face, neck and anything else so affected, the adjust the slider bars, I find bringing the brightness down, often lowering the shadows, increasing saturation and sometime upping the temperature just a bit can do wonders. This applies to any work that results in an unrealistic face color, not just the swap.

2) You get much better results if you go straight to the swap function and do that, adding any additional edits only thereafter.

This app has always been pretty out in front of the pack, and recent updates have been impressive in my book.

Taylor Swift and Debby Ryan
           

OMG .... that 1st pic of taylor swift really suits her a lot ... perfect fit for her

Lily Collins, Cara Delevigne and Elle Fanning

(December 9, 2020, 4:15 pm)ADC12-X9 Lily Collins, Cara Delevigne and Elle Fanning

Amazing! nice work mate!

Dumb question, but which tool on FaceApp?

(December 11, 2020, 1:03 am)Bob1990 Dumb question, but which tool on FaceApp?

The tool is called ‘Face Swap’

(December 11, 2020, 1:03 am)Bob1990 Dumb question, but which tool on FaceApp?

Weird - I am trying that and when I do it comes out as some morph of the two photos instead of a direct face swap of one photo to the other (no, i'm not using the 'morph' tool).

How do you save it without the 2 images that you used being in the corners?

(December 12, 2020, 4:03 am)Bob1990 Weird - I am trying that and when I do it comes out as some morph of the two photos instead of a direct face swap of one photo to the other (no, i'm not using the 'morph' tool).

The app doesn’t always give you a clean result but when you end up with a face blend instead of a clean swap it could be the result of two things:

1. The photos do not contain enough data for a clean swap

2. The facial structure of the original face is too different than the face you are attempting to swap it with

In both cases the app will do its best to complete a swap but the result ends up in a mixed face. 

If one photo doesn’t work try another one. You may have to experiment with several photos before you find one that works correctly.

Hope this helps.