The Spark is only intended to work with the VivoKey platform. It’s intended to be a cryptographically secure identifier that will replace logins and passwords for a variety of services. Some current goals are access control, One-Time-Password generation, PGP message encryption, and eventually MasterCard transactions.As the number of VivoKey products and integrated services grows, it will continue to gain utility.
The xNT and flexDF are more intended to write small bits of data (like a URL, contact info or a WiFi password) to, and will also spit out their unique identifier (UID) when scanned by a phone. I use my flexDF to unlock my phone and I used to use it to unlock my car (but it was rather finicky). They’re fun, but their uses are limited and they really don’t provide any security beyond physical distance.
There are pros and cons to both. The Spark might not be able to do much yet, but it will continue to grow throughout this year and into the future. Soon enough you’ll be able use it to unlock your phone, but in a truly secure way. It will also be plug-and-play. There is a small barrier to entry with the xNT and flexDF because you need to learn a bunch about the tech to manage it yourself.
If you want to do some stuff with your implant right now, you could consider getting one of those other tags. Truth be told you can just buy a NTAG216 sticker for $1 online and stick it to your pocketbook to get the same functionality. Implanting a VivoKey product is becoming part of an ecosystem.