My experience is that the client deployment tool is hit or miss. It requires that the remote registry service is started, and who has that set? That default setting changed long ago.
The GPO, Computer Startup Script (not User) is best in my option because if someone uninstalls it, it will re-deploy it. I’ve shared the script we use and it is around here somewhere… Let me look.
… here we are: Logon script to install BigFix Agent