Are you talking about something like
this?
If not, not quite understanding what you mean by refiller.
If so these bottles are quite helpful. You can screw the top of one into your mod's 510 connection, refill a squonk bottle using pressure and gravity. It keeps from needing to take a squonk bottle out & maybe making a mess.
Here's a video that might explain.
Not sure if they have a similar product to refill RDTAs (tanks). Reckon there may be such a thing. Not seen any myself. It might be rather handy if they did.
I got away from using tanks in part due to needing to be dexterous, coordinated to refill them. Would often juggle a tank in one hand and a juice bottle in the other.
Difficult having that focus when a body can go whack at times. Nerves sometimes have a spasm inducing misfire for me. In part some due to congenital issue/s, in part from having lived a wild run of life.
As to why some might suggest disposables? Maybe as a quick way to try vaping out without so much upfront investment. I might could see that if someone was "on the fence". Still suggest a fairly decent kit to start out. You can get decent kit for about $30 USD, just hardware.
Then, if you want you can "move up" to a better more durable kit for a bit more. Until you get like me spending about $100 each for a few different medium to high end mods. I got those because they're durable and decent quality builds. The two Signature Tips mods I recently got both "feel" good too.
Then again, it might be disposables are being suggested to drive away newbies too. As Churchill was found of stating, "nothing ever happens without a plan, or motive behind it. And that is usually political of an ends." Paraphrased of course, he was more succinct yet robust.
As to driving newbies away, what ends? Well send them right to or back to regular cigarettes of course. I'm sure you'll soon find out a lot of the "platforms" take kick backs from Big Tobacco, in some manner.
Greed keeps the Earth's largest payroll.