Should I use a bridge (single user base) in DataLife Engine?

Question

DLE

Should I use a bridge (single user base) in DataLife Engine? Anyone use this feature?
In particular, we are interested in the following. questions:
1. How did you decide to display avatars? As far as I understand, the avatar (profile photo) is shown only on one site (on which it was uploaded), and on the second it is not, since the image file is located on the first site.
2. Will user groups be separated? That is, one site has its own groups / user rights, and the second has its own.
3. How safe is this bridge?
Or are there other solutions for single sign-on between DLE sites?