Well written article about low-e window film at grist.org.
The author sidesteps the issue of endorsing the film on home improvement stores in the original question. Low-E film is a very specific type of window film. It is best to purchase it from a reputable brand like SolarGard, Llumar, SunTek, etc… rather than using the non-professional brands from home improvement stores.
The article also states:
Low-e films should last about 10-15 years, can save you up to 10 percent of your electric bill, and can be applied without too much trouble on a small window but should be professionally smoothed on a larger window.
Window film application is not rocket science as demonstrated by this home tint installation video. The most common error is not using enough of soapy water between the film and the glass. Without enough of this barrier, the film cannot move and slide into place.
The rule of thumb that we have been advising DIY window tinters is that any normal sized window that is less wide than your arms outstretched would not be that difficult to tint. Windows wider than your arms outstretched will be easiest with two people.