I believe I have as much experience with a Sightron scope as anybody, other than the fellas that run the company. Sightron is based in N.C., and founded by three ex-Tasco guys (don't hold that against them!). Their scopes are built under contract in Japan.
I'm a value shopper, and although lots of guys will give you anectdotal bullcrap about optics, most of what you "hear", both good and bad, is probably just third-hand rumors.
I selected a Sightron because I was intrigued by their ads in Precision Shooting magazine, and decided to find out for myself if they were a pretender or the real deal. I bought their SII4016x42MD, which is a one-inch tube scope, 4-16 variable w/adj. objective, target knobs, fully MULTIcoated optics, and a mil-dot reticle (which equates to standard spacing when set to just below maximum magnification on my scope).
Summary of performance: My Sightron is mounted on a Rem. 700 VSSF in .308. This rifle is used in long range competition, including tactical matches from 200y-1,000y, F Class, and 600y and 1,000y NBRSA events.
In my tactical match, the scope is adjusted through 22 minutes, which means 176 clicks (it has 1/8 moa adjustments) from 200y to 800y, and then back again, for a total of 44 moa elevation travel, and whatever wind is required.
I've been using this scope in competition for more than 2 years, and it has witnessed about two thousand shots. It's mounted in Leupold standard rings on a two piece Millett base. My scope runs out of "up" at 800y, so I use the mil-dots for holdover at farther distances (with very good results, luckily).
No other scope that I've used is as repeatable as this Sightron. I own(ed) and use(d) Leupold Mark 4, Leupold Ultra, Weaver V and Grand Slam, Nikon (another good value) and others. Sightron's repeatability is better than any of the others, in my experience.
Clarity, waterproofness, it's all there. (They might not have quite the clarity of Nikon, but that's nitpicking.) We shoot rain or shine, in dust, mud, and wind up to 40 mph on bad days. So far, this Sightron has met any challenge you could reasonably tackle.
Other items worth a mention: my factory Rem. 700 VSSF is an exceptionally good (factory) rifle. With the Sightron aboard, my first two five shot groups at 1,000y were 6.25" and 9.125". Beginner's luck perhaps.
I've also lucked out and put 3 shots into 4" for a 28/1x (out of 30) at one thousand yards during our tactical match, and 3/3 shots into 2.5" inside the head of a B27 at 600y in the same match. This same outfit, if I could read wind a bit better, could certainly clean the 600, 800, and 900y stages of F Class matches.
The scope *will* perform, if my experience is typical. Buy one, and I think you will be glad you did.
I do not know how their newer 30mm tube scopes work, but I do know they cost quite a bit more. If you don't need the extra elevation they would provide, or if you use a forward tilted mount or rings, or can adapt the mil-dot reticle to your needs, you can probably do just fine with one inch tube.