This is just my personal take on it. Mouth to lung on anything airy, rda, rta, rdta etc doesn't work. At least not for me as an ex smoker. Typically mtl setups involve an rta with tight airflow, small diameter chimney and restricted drip tip. Many claim to be dual purpose but they seem to fall short, being too airy for true mtl and too restrictive for comfortable direct lung inhales.
Just from my own conclusions, larger diameter chimneys with wider airflow holes/slots don't work and make me cough. There's too much volume and a 'drag' as in the type of puff a mtl smoker takes involves drawing the vape into the mouth, then inhaling. The mouth is only so large, much smaller than the capacity of lungs inhaling deeply. By the time any actual vape gets into the mouth with the airier setups the mouth is full of empty air and little vape because it hasn't had a chance for the vape to travel all the way up the chimney yet. That's what seems to gag me anyway, it's like fresh air taking a breath or smoke/vape, one or the other not half and half.
If you're looking for something more like a cig you may want to check out something like the kayfun v3.1 or kayfun v4. It takes a little bit of adjusting the airflow, it has to be done with the atty off the mod via a tiny (I mean TINY) screw in the center behind the 510 pin. Once you have it set you shouldn't have to mess with it much. The kayfun v5 is too airy for mtl (just my opinion). Even the v4 seems a little 'airy' compared to a real cig, there's quite a bit of restriction on a real cigarette. Between the packed tobacco and the filter (assuming you're used to filters) vs no filter of any kind on an rta.
I'm using the ehpro bachelor and it was supposed to be dual purpose, it's not. I ended up learning how to direct lung since it's different than the way I smoked. The amount of vapor is satisfying, it's a single coil and easy to build on. It's just not a mtl tank and it's not as wide open as many other rta/rda's out there especially those with the wide bore chuff caps style tips.
If trying to get the same type of sensation as taking a drag using vapor the closest 'feel' I've come across are cigalikes. They have tiny air slots and a pinhole chimney but the vapor production is poor as is the selection, the battery life and cost of using them (factoring all the replacement cartridges).