They are two different products, as you know. I have tried both. M20 is a light cleaner wax (AIO). I have been impressed with it. It cleans the paint (it removed some water spots that had recently formed), and it's darn easy to use. I would describe M20's "look" as bright. NXT, on the other hand, has a somewhat different look. I guess I would describe it as "wetter." I think. These are my subjective impressions, and memory is a tricky thing. I have never tried comparing the two products side-by-side. Also, some folks seem to have problems with streaking with NXT--this streaking seems to be caused by folks either applying NXT too thickly or removing it too quickly. Apply NXT thin and allow it to dry 30 minutes before buffing it off.
One other thing, you might consider applying M20 and then topping it with NXT (or any other wax you'd prefer).
I like M20 and judge it to be under-appreciated. I am not as thrilled with NXT, though. I like Mother's Reflections, available from Amazon.com, better; but my favorite sealant is Blackfire Wet Diamond. But if you're presently restricted to over-the-counter waxes and don't want to spend more than $20, then try NXT, Gold Class Carnauba Plus, or Duragloss 105. If you're willing to spend a bit more, you might consider picking up a tub of AutoGlym High Definition Wax at WalMart. I understand it's selling at around $35. This may well be the best premium carnauba wax now readily available through OTC channels.
