Got a FasTrak Transponder at Costco in the Los Angeles Area today. Unfortunately, these are locked to LA and cannot be registered in other areas, such as the Bay Area. The reason why you want to register it with Bay Area FasTrak is that they have zero monthly fees. Once it is registered, then you can use it anywhere in California. Like my HOV stickers, I won't be using it in a consistent manner, maybe never. I don't want to pay monthly fees for something "just in case". Also note that LA Metro recently revoked FastTrak HOV CAV privileges for Teslas which pissed me off. Bay Area FasTrak said that the transponder could only be registered with Metro FasTrak (the verification "code" will not work) and you can't take the transponder back to Costco. To try to send the FasTrak Transponder back, LA Metro said to make an account just to return it. I told them I would just toss it (after destroying the transponder). I am now waiting for Bay Area FasTrak to send me a Bay Area "locked" transponder. We will see how that goes.
I frankly hate these "Lexus Lanes" transponders.