New to this lifestyle and dont know where to get started

[Pilgrimsmaster]

@BRowl

Is there any other difference between them that stands out?

Effectively they are very similar.
NExT uses NTAG216 1kB (888 bytes) of user writable memory
The NExTV2 uses NTAG I2C Plus 2K so it has double the storage at 2k BUT the other 1k is not quite so easy to use because only the first 1k of memory is accessible for NDEF data.
You can read and write data to sector 1 with something like NFC Shell with special commands.

So what happened with the 2k memory on the xSIID?

TL;DR - The first batch of xSIID made December 2019 were formatted to try to use all 2k of memory across two 1k memory sectors for NFC applications, but the NFC stacks built into Android and iOS phones don’t know how to properly read multiple memory sectors in NFC Type 2 chips. Future batches are formatted to only use the first memory sector which is 1k for NFC applications. The remaining 1k is still readable and writable by phones, but only with a custom smartphone app that can directly address…

I’m pretty sure the NTAG I2C Plus 2K chip was inly chosen for energy harvesting…aka Blinky

So, other than the Blinky the difference is negligble.