Dedicated vs GPON

AT&T just started offering GPON in our area. We currently have a 100/100 dedicated fiber. We can switch to gigabit GPON for a little less than we are currently paying for the 100/100 connection. Does anyone have experience with AT&T’s GPON service reliability and is best effort gigabit equal to or better than 100/100 dedicated. The reason we are looking to upgrade is our guest network is constantly being overwhelmed. We also have a 100/100 Charter fiber I can put our VoIP system on but if it fails it would switch to the AT&T so I am still a little concerned. Even with qos how is the reliability/stability of a GPON.

Thanks for any advice/experience with this.