I'm blessed to know Bob Backert personally. He is one of the kindest, most. centered persons I have met. He has been transforming my Conrad Johnson PV-12L for the last few decades. I wouldn't give up my rig for any other line stage! Yes, the classic warm glow of the cj is gone but the holographic wall to wall soundstage, often attributed to a tube stage is still there. More transparent, open and revealing than stock. Bob's big emphasis is on the stability and robustness of the power supply. He used to, and maybe still does refer to it as the "Greenforce Power Supply" for which he has the patent.
I know nothing of the Zesto product so can make no informed comments about it.