I've seen this product in a local hobby store, now what's with this chemical? Can this be used as a sealer for inkjet printed decals?

Shonen I actually don't know if it can be used to seal decals made for inkjet (I personally don't think so because you have to apply it by brush andn this quite likely will cause the ink to run). What it's great for is when you have old decals that risk to fall down in pieces once put in the water; Give a coat of liquid decal film and this risk is avoided! Another use is to give consistency to the decals printed with wax/resin inks on plain decal paper (I mean the one who has got only a glue coat and not a film carrier).
Ciao

You can't use it over inkjet decals, but I have used it to seal inkjet produced paper "decals" or wallpaper, such as the shirt on the scarecrow in my Brothes in Arms vignette posted elsewhere here. There may be a decal paper for injets, but the one I used last summer was not the one.
And as Fabio points out, it's prime use is saving old decals. It has the advantage of adding virtually no increase in thickness and responds wery well to Microset and Microsol.(At least MicroScale's version does.)

So can liquid decal film "strengthen" those Airfix decals? They are very fragile and just putting them in water causes them to break