I used to use Clockology some time ago. It is ok, it does not harm anything. I just see, that it is still on my watch...
They have "internal" watchfaces in the app and it is a quite active community. There are also sites with not so legal copies of well known watchbrands, you can load via the files-app. I stopped using it. If you like crazy watchfaces, which are sometimes not that bad, then you have a huge choice of almost everything.