mmm... I have used NXT as well being the first upgrade from kangroo/turtle and i was impressed by the results on silver. Here is my very first session with NXT:
https://www.pakwheels.com/forums/body-work-interior-paint-glass-appearance/207170-car-care-detailing-dreams-part-2-a-165#post3847054
While the pictures were captured with a cell cam, but to the eye it looked like a great upgrade. The only downside for NXT to me was that it wasn't durable and the "looks" lasted only a week (while the protection may have stayed there). The upgrade to Meguiars ultimate wax was also good from NXT since it was more durable. Meguiars ultimate wax is more versatile of the two and should do great for both your black and silver whereas NXT would be more better suited for lighter/metallics. But the key to getting good outcomes is having a well prepared surface (clay, cleansed). I used both of these for a couple of times and by that time I had gotten addicted knowing theres a whole sea out there that I should get my hands on and then there are some great choices you can make from various proven brands like Klasse, Wolfgang, Blackfire, Optimum, Pinnacle, DP etc (depending on your preferences e.g. the look you prefer, the money you're willing to spend etc).
My office is in G-10. Feel free to drop by some time if you're interested to know more and we can have a discussion over a cup of coffee .