I was heavily involved in USPSA/IPSC in the late 80's through '99, during the era of the first RDS on open division pistols. I have a huge amount of otherwise obsolete experience with RDS's to share! Jerry Barnhart won the nationals mounting a Tasco PDP1 and the race was on (late in the 90's he began competing with early Bushnell holosights, or what is now Eotech). NOTHING lasted back then. At my first nationals I had one Aimpoint (5000?) on my pistol and two spares in the range bag. On the trip home the last spare was in the pistol's mount.... The dots just were not reliable enough to be on a two way range. However, competition has a way of developing technology...
As I recall the first reasonably reliable RDS solution was a setup by Dave Dawson where he dovetailed the side of a Tasco PDP2 to match a mount he made. The theory was you could have two scopes fitted and pre sighted for a spare, but the mount on the main body seemed to improve reliability over mounts that employed rings on the front and rear tubes. It was also widely accepted that a failed scope sent back for service came back much more reliable as the repairs were hand done and wiring was reliably repaired...
Ira Kay developed the SeeMore next and it was not universally accepted at first. Initial units had some development problems with reostats loosening up and other issues, but the sights were practically dead nuts reliable. Todd Jarret was an early supporter of the sight. The major issue most of us had in transitioning to them was losing the tube reference of a traditional scope. In effect, the tubes allowed us to be sloppy with our draw and presentation, as the tube provided an instinctive alignment of the pistol with our eyes when addressing the targets. Unfortunately, that was slow. The SeeMore forced us to harden up our presentations of the pistol and get more consistent, once that was accomplished our times improved noticeably, and combined with the reliability of the units, the SeeMore soon became dominiant. It was still a common sight to see a shooter, particularly in an awkward position, doing the "SeeMore Dance" rotating the pistol around a downrange axis trying to find the dot... we learned quickly to pick up other indexing points on the pistols....
Tasco went bankrupt and Aimpoint got serious. They came out with their Comp series of smaller and more reliable dots and a devoted following stuck with them, not the least of which was Rob Leatham (a future, if not current, legend on the order of Ed McGivern [sp?]). I think many people liked the Aimpoints because the tube sight gave them that instictive alignment that was so hard to acheive with the SeeMore on a pistol platform. That issue is never a problem on a long arm, since the stock and eye alignment are all part of the system...
I cannot comment on the SeeMore in combat, but it was a reliable sight in competiton. It is hard to order a SeeMore with a rifle appropriate dot size, as you normally have to order the module for the smaller dot seperately. Still, the economics are attractive, and the ergonomics with its uncluttered FOV are very attractive. I think the body is a bit long, so there may be rail space issues with some platforms.
While active in IPSC I shot an estimated 250,000 to 350,000 rounds in practice and competition. I replaced or reparied a lot of Tascos and Aimpoints (NOT current milspec), but I never had a SeeMore go down. Based solely on competition experience, I would not hesitate to use a SeeMore on a serious carbine if the rail space was available. Note, however, that I have not mounted or used a SeeMore on an AR platform myself.