When condensation forms inside of an IGU (Insulating Glass Unit) it means that there is a rupture in the seal and that air and moisture has penetrated the space - this is true in the almost all cases.
The folks who claim that they can install a one-way valve in the IGU that will allow moisture to escape and dry out the interior of the space – thus eliminating moisture-caused condensation between the lites – have some validity, but can you spell “gimmick”?
While their system will give the appearance of having eliminated the problem, in the right environmental conditions simply drilling a small hole in the glass, even without their cool one-way valve, can give the same results without the expense of the visit - again, in the right environmental conditions. Now I am definitely NOT suggesting or recommending that anyone should try drilling a small hole in their IGU in order to “fix” it. That was for example only.
Ultimately, a blown seal is an aesthetic issue. An IGU with a seal rupture will have virtually the same energy performance as a sealed unit assuming that the original window did not have an argon gas fill. If the IG had been argon filled, the blown seal has or will affect overall performance since the argon has escaped. But in the case of a simple 2-pane clear glass IGU, the blown seal is not a performance issue.
A blown seal allows outside air and moisture to penetrate the air space of the IGU. This is generally a very slow process. The “clean the inside of the IGU and stop the fogging” systems result in a much faster air exchange rate within the IGU space. This rapid air exchange allows the air/moisture level in the interior of the IGU to more closely match the air/moisture level to the exterior.
While physics 101 teaches us that warm goes to cold and moisture goes to dry, the “clean the inside of the IGU and stop the fogging” systems will help the interior of the IGU stay true to that idea. Physics 101 also teaches us that warm air expands. The one way valve does allow the expanded air to vacate the space taking much of the moisture with it. The “clean the inside of the IGU and stop the fogging” call this process "IGU breathing" - or something similar. It really does happen and it is the reason that the systems work. But remember that it is a cosmetic "fix" and it still doesn't address the probelm of the bad seal.
Anyway, drying out the airspace helps the interior moisture level of the IGU to remain above the dew point thus preventing the formation of condensation on the glass surfaces between the lites. Sounds like a good idea, but in some sense it is like placing a band-aid on a bleeding artery since it can cover without addressing the actual problem.
If the original IGU had argon fill, the gas is gone. If the original window has a LowE coating, then that coating may eventually corrode. The de-foggers will do nothing to prevent that. The original moisture seal is still and the “fix” doesn’t address that issue in any way. And IGU's cannot be successfully "recharged" with gas in the field, despite what some of the “clean the inside of the IGU and stop the fogging” companies claim.
And finally, this “fix” isn't necessarily cheap. The “clean the inside of the IGU and stop the fogging” folks will tell potential customers that their process is cheaper than replacement, which it probably is, but as mentioned earlier, performance may be very dependent on environmental conditions. Some people may use one of these systems and be 100% happy for years. Other folks may see the same or other problems relatively soon after the "fix".
And finally again, remember that this is ultimately a cosmetic issue. From an energy performance standpoint it doesn't have to be fixed right away.