What is NPS (National Park System?)?
I'm wearing jeans out in the field because I need something that breathes well, keeping me cool (wind over wet jeans and shirt cools me down for the summer). I cannot wear synthetics out in the field during the summer because it is just TOO HOT. The opposite of what I was telling customers when I worked at REI altogether for ten years. I have probably 15-20 years' supply of synthetics from REI, like the t-shirts, cargo shorts and pants, etc., but I only wear them around town because I want to wear them out before I pull out the really good stuff from Tag Safari (I did the same thing with them, fearing that they would disappear on me before I would have the chance to stock up, similar to Banana Republic's lineup change to office work apparel, which I failed to act on before the change).
I had the cheap jeans from that mall place in Houston on the extreme west side off Hwy 6. Bitten Jeans? At any rate, they were wearing down in the two years I had them, and boy, they dived to nothing in less than a year on a ranch and a farm. Three years, max. I usually go about 5-7 years on jeans. Now, I've got the Levi's with minimal stretch, as opposed to maximum stretch with the Bitten Jeans. They'd stretch out 4 or 5 sizes within a week of wearing them (space and laundry resources are very limited, so I have to wear two sets of clothes for the entire week in the field), and I could pull them RIGHT OFF without unbuttoning them.
Anyway, the Vertx pants seem to be an interesting style, if you are of the tactical mindset. Nice pants. I would have been ALL OVER them 5 years ago when I lived with such a mindset because of the colors available. So, here's the safari style, the tactical style, and what I call the REI style (simply because they are available at Academy, REI, Bass Pro Shops, Gander Mountain, Cabela's, being brands like Columbia, Kuhl, Prana, Royal Robins, Mountain Hardware, and several others I'm forgetting in my year after leaving REI).
Edit: Almost forgot - jeans would not be the best option for metal work because of sparks from welding and machine work around snaggy objects. I've had that happen at REI of all places, just because I whipped around a fixture and ripped my jeans on a fixture that had jagged metal. Another issue that I would have with synthetics is that they're noisy in the outdoors when you're moving around in them, which spook animals you're trying to get up close to for photos.