AVF;
The short answer to your question is........"it all depends".........on so many things........all of which vary greatly from individual to individual.
This is an issue that I have been interested in and researching for several years now; I almost ordered my first Glock, (a G34) shortly before it was announced in the 2014 Annual Buyer's Guide that Glock would "shortly" be offering three of it's existing pistols, the G-34 / 9mm, G-35/.40, & G-41/.45, in addition to the all new G-40/ 10 mm, in what they refer to as "MOS Configuration", (with MOS being Glock-speak for "modular optical system"), As I was already greatly interested in reflex sights, (inasmuch as many top competitors had been using them for some number of years already), I immediately intensified my reading-up on this subject in order to determine if it would be to my advantage to hold off ordering a new pistol until these new MOL "configured" models started shipping.
I quickly realized that starting out with a pistol that already had the slide milled for mounting a red dot sight would indeed be very advantageous, so I told my LGS in Terre Haute that I wanted the FIRST G-34 MOS that they received.
It was a fairly long wait, but as I was in no great hurry, and inasmuch as I was still a long way from determining exactly which red dot sight I wanted to buy, the long wait for the pistol afforded me an equally long time to research this subject further.
There are probably at least ten times as many things involved in building and marketing a red dot sight that will be robust, accurate, and totally dependable than most people realize. I quickly found out that with red dot sights, (just like all optical and electronic goods), you generally tend to get "just what you pay for".
There are many red dots selling for, from less than $100 to maybe $200 that I won't comment on; (in mentioning that, I have just incurred the displeasure of everyone who has ever purchased a red dot in this price range, and all I can say is, I'm sorry if you feel that way, as I'm merely attempting to be objective. Once we get beyond the $200 and into the $300 range, we find the Burris Fastfire || & Fastfire |||; This is the first red dot that I was able to actually look at, handle, and discuss with many who were already using them; IMO, Burris's Fastfire ||| is probably the biggest selling and the "most liked" by the "most people", probably because every LGS I have ever been in has them in stock, and a tremendous number of them have been sold, with a large majority of the people owning and using them being quite pleased with them.
However..........I seriously doubt that you will ever see this red dot used in combat, upper-level competition, or by the many people who have the "budget" to buy a Trijicon, Leupold, EOtech, Aimpoint, or other "top-of-the-line" red dot sights.
Are these premium red dot sights "worth" their higher costs? Only you can answer that; ( an awful lot of people seem to believe they are indeed "worth every penny" they cost ). A lot depends on how you intend to use a red dot sight; You state that you need it for a new Glock 10mm; consider this; ANY red dot sight that is "slide mounted" on ANY semi-auto pistol needs to have it's electronic circuitry robust enough to stand up to the constant (and quite violent) cycling back and forth of the slide that it's mounted to; on a 9mm semi-auto that's a very demanding "environment" for any electronic device to operate reliably in; the same red dot mounted to a 10 mm has an even more punishing environment to maintain it's reliability in! In fact, you'll probably note that when red dots first started to be used extensively in competition, (and due to the "state of the art" at the time I'm guessing ), many competitors had their red dot sights frame mounted on mounts that sometimes cost as much as the actual red dot sight, but with the red dot not being subjected to the violent "back & forth" cycling of the slide.
The next big issue that many very experienced gun owners quickly realized was, "we want our red dot sights to be co-witnessed with our steel sights"; This in one area, (IMO), that the gun owners were ahead of the red dot sight designers! Most red dot sights have a relatively small "window" (most of which tend to be some distance ABOVE the level of the slide ); again, IMO, the single red dot sight that stands at the top of the heap in this regard is Leupold's Delta Point and Delta Point Pro; (and to the best of my knowledge Leupold is the only maker to offer a red dot sight that uses a tiny red "triangle" rather than a "dot", and both of their red dots have a very large, very low windows, thus making it easier to co-witness with the pistol's steel sights.
