I asked a similar question…
I am PLANNING on getting the Flex One as soon as it is released.
Is there any ACTUAL reason to have more than one Vivokey, especially when one of them is a Flex One
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AMALS ANSWER
The first reason to have more than one VivoKey would be to maximize your compatibility… for example, I will probably get both the Spark 1 and Spark 2 implanted because I want an ISO15693 chip for using my Quicklock padlock and Gunbox storage case, so why not make it a Spark to boost utility.
We will soon be updating the platform to allow you to have more than one VivoKey chip associated with your profile. A very good reason for having two (or more) VivoKey devices associated with your profile is to make a kind of “back up” access method. You will be able to access your profile and perform authentications using any of your chips, so let’s say you smash your Spark 1 or it stops working for some reason, you are not locked out of your profile and all your apps and services. This will become much more important as we release new services on the platform like the VivoKey Vault… so it’s a good idea to have backups. I will.
Ummm, why would you take it out of the sterile syringe??? 
If it was my decision, I would put the OG Spark in a less preferable place, leaving the prime spots for implants you will use more often.
I would also read this, where again somebody asked another similar question.
The decision is yours, but,
Hope that helps