Megs NXT is a sealant/wax blend rather than a pure wax. It contains soime mild cleaners to clean the surface while your applying it.
Normal routine like you say is to polish and wax or polish and apply a sealant.
Polishing cleans up the paint, wax or sealant locks in the shine and protects. In general a sealant will out last a naturual wax in the time they leave your paint protected. (30 days for a wax, 30 - 120 + days for a good polymer sealant) but the downside is they never look quite as good a a natural carnuba wax.
or this reason lots of people polish, use a sealant for protection, and then add a Carnuba Wax on top just for looks.
Hope this helps.
Rich