Okay so lets clear this out once and for all. Almost no one is wrong here, just a small tid bits of confusion from what I see.
So most synthetic waxes are made from the same compounds that make sealants by the same company. As safdar bhai above explained megs m21 is the pro version of the nxt. Obviously since NXT is a consumer product and M21 a professional series the products have different requirements, ease of use, etc
The other thing that everyone needs to realise that paint sealants come in a wide variety.
Wax based. Most synthetic waxes fall under this category and are boderline sealants, since they dont have the typical "sealing" ability/ longevity.
Water based sealants: Very good examples include the Wolfgang Deep Gloss Paint Sealant. Excellent quality, very easy to use and long lasting.
Acrylic based sealants: Klasse Sealant line. Excellent quality again, very good life, though a little tricky. takes one or more time to get a hang of it
Nano coat sealants: Carpro Cquartz and Dodo juice Supernatural infinity paint sealant: Excellent quality stuff, extra long life but obviously expensive as well.
Permanent paint sealants: Optimum opti-Coat 2.0 permanent paint coating. This is absolutely the best protection one can get but the most difficult to apply. Longest life and the toughest barrier. Most expensive as well.
Hope this long post solves out the confusion 