What apps are safe to use that provide additional watch faces?

Hi oakfan1108.

Re: Apple Watch faces and their features:

The only Watch faces that I know are safe are those from Apple.

You might want to browse these two articles below.

You can choose your iOS at the top of the pages that open from the links, for accurate info,

(NB: You can customise most watch faces).

Apple Watch faces and their features – Apple Support

And / or

Explore the Face Gallery on Apple Watch

When you find one that looks interesting, 

you can customize it, choose complications, 

then add the face to your collection—all from the gallery

Explore the Face Gallery on Apple Watch – Apple Support

All the best :-)