Welcome back!
Do you already have any implants?
Depending on the type of tag you might be able to get away with just your phone, although the PM3 and Flipper Zero are also popular choices. The PM3 is my personal favorite, and the most capable
It’s possible, but it’s hard to say without knowing a bit more about the systems you’re hoping to use it with:
There’s not enough info (for me anyways) to tell exactly what technology that fob is, could you try scanning it with your phone using an app like NXP’s TagInfo or NFCTools? That should give us an idea what you’re working with
Realistically, the NExTv2 will have two credentials on it. The NExTv2 is a dual-chip implant, and both sides can be used simultaneously, although they aren’t cross-compatible. The HF side doesn’t support cloning, it would have to be enrolled in any system you wanted to use it with. The LF side however does support cloning, and so would likely work for you if your system is LF
Additionally, although it only holds two credentials at once, there’s no limit to how many different systems each credential can be enrolled in at any given time, if you’re capable of enrolling new tags into the systems