The Overlord monitor is indeed an overclockable monitor. This is not one of those sketchy ones that are only advertised as overclockable, it definitely is overclockable. It does not drop frames, and it does full pass show all frames that is sent to it.
The proprietor was actually one of the very first who was able to get his hands on a Catleap "2B" - these are custom engineered from that stock, not the current stock of Qnix/X-stars.
I can't agree with you though, on "test it to its limits, then sell as is". Intel doesn't do that. Video card manufacturers don't do that. And there is so much in the pipeline that affects the ability of any single monitor overclock that it's impossible to guarantee it. Video card, cable, port, drivers, even ambient temperature - all of these are also issues that affect your overclock. It's like saying intel should guarantee a specific (4.4? 4.5? 4.6?) overclock for i7-4770ks or else you won't buy it. No, that's dependent on your motherboard, power supply quality, cpu cooler, ambient temps. That shouldn't stop people from buying 4770k's (or 4790k)
The Overlord monitors are tested to 120hz - they can't guarantee it since it's impossible for the monitor to work out-of-the-box at 120hz. Even if the above physical factors are accounted for, it still requires a circumvention of the software limits that are already present on your computer, imposed by Nvidia and AMD. In the end, the user must circumvent these software limitations on their own.
In any case, don't think of it as a 120hz monitor. It isn't. Think of it as a 60hz "k" series monitor. You pay the premium (is it, really?) for the ability to overclock your monitor beyond what it is normally capable of.