Use what you like, but they aren't a gimmick:
1. Glass is generally non-reactive with a lot of acids/compounds, so by using glass for storage you don't have to worry about a lot of things. Depending on the ingredients this can be a pretty big deal, but for others notsomuch.
2. Nicotine is photosensitive, or reacts to light, so when exposed to light it'll gradually turn brown and lose potency. Similar things may happen with various flavorings.
Though for #2, while clear glass can block
some rays, you really want amber bottles to be blocking most of the UV (ultraviolet) and such.
For an example, this is actually why beer generally comes in green or amber bottles -- without it, light over time causes it to go "skunky." The UV rays break down acids in the hops, which then react with sulfer in the beer, which then makes it smell kind of like a skunk. How this would translate to eliquid depends on the flavorings used.
Green beer bottles exist due to a shortage of amber glass in WW2, primarily because "premium" european brands wanted to separate themselves from the cheaper beer using clear bottles and now it's just their branding. You'll also see blue glass, which has cobalt oxide or carbonate mixed in.
Out of them, amber is the gone to use for long-term storage as it has the best UV protection, followed by cobalt blue and then green. How and when they're appropriate is up to the user and their needs, but yeah not a gimmick.
*gives the horns*
