A closed system is pre-filled pods. I started a while back but I bought a few on the cheap for grab and go stealth vaping at the movies or whatever. Mostly if it's a pod I get open so I can change flavors and vape what I want.
Having said that, recently, I saw a Youtube video where a guy was saying we are creatures of habbit. People puffing on closed pods are stillgoing to the gas station like they used to, just getting a different product.
I can relate to that because when I first started, it was the little KR 808 e-cigarette. The one that was painted and sized to look just like a cigarette. Those would be good with nic salts. The habbit was totally different though because you cad to get your juice out and drip this little cartomizer making a mess in the front seat of your car where batteries and chargers and 10ml e-liquid bottles are everywhere.
I saved buckets of money so I did both for quite a while because of the quick light of a smoke. "Oh snap, my battery done died and I left my charger at home!". No matter if you vape on big rigs or even smoke tobacco, having a few disposables \, your get that quick light up. If yours dies and you pass a gas station, I would like my favorite flavor to be there.
I have about 100 setups of a different ilk. Now I just end up having about 5-10 batteries in different states of charge with a variety of drippers and tanks so I can switch flavors often. That is the best way to keep away flavor fatigue.
Open pods you buy coils and you can change out coils and add juice. Closed pods you buy a new pod with coil and juice and is all ready to go when you drop head in battery. I do refill closed pods on my Vype Epods but have not changed the coil yet. Almost anything can be rebuilt or refilled. Pods are like old technology low wattage and higher ohms coils just with high nicotine and salt added to make it smoother. I am putting Nicsalts in my old mechanical with Kayfun Lites that I vaped years ago. They don't blow big cumulus clouds. 30mg in nicsalts and 6mg freebase in my big smoke machines. They seem to be pretty close with how I feel since testing with nicsalts the past two weeks. Utube is your friend. CHEERS!