The naming conventions are a bit weird until you break them down.
XPS: Sits at absolute co-witness height
EXPS: Sits at 1/3 co-witness height
2-x: Does not have NV brightness settings
3-x: Has NV settings.
Pros: Big window to look through, circle-dot can be very fast for closer targets, 1 MOA dot can be good for longer shots, holographic image might be better for those with astigmatisms.
Cons: Big and heavy (relative to a smaller Aimpont-type optic), shorter battery life if left on (they may have shake-awake now...I can't remember), can have delamination issues on the glass (but optic will still function fine).