All things being equal, yes you'll get the same amount of vapor out of different 3.7 v devices. But all things are not equal. There's differences in the circuitry in most PV's. Choosing a different resistance on your atty will make a difference. All batteries are not created equal either.
An all mechanical mod, like the Omega has no real circuitry. This means less resistance, as in more power gets to your atty. Most mods use switches and wires, and even the best designs introduce resistance. And if the mod designer chose a switch with a 1 amp rating you won't get the power you need at the atty.
Atomizer resistance makes a difference too. The lower the resistance, the faster it heats up. It'll burn hotter too, that's what makes it give off more vapor. Choose a 1.5 ohm atty @ 3.7v and it'll produce more vapor than a 2.0 ohm atty.
Batteries come in different varieties. Most everyone uses li-ion batt's because they're compact, have good capacity, and are at a decent voltage. But there are different types of li-ion batteries. You always want to use protected cells. But there are also low drain types, and high drain. The low drain discharge slower than the high drain. Most cheap li-ion batt's are low drain, and most people don't know the difference so that's what they use. But put a high drain in the same mod and it'll produce more vapor.
So in summary, if you want to get the most vapor you can out of a 3.7v device use an all mechanical mod, or check the specs on the circuitry if it's not mechanical. Use LR atty's. And use high drain batt's. If you use this combination you'll be surprised how much vapor you get. I was considering a variable voltage mod until I got the right combination in my Silver Bullet. Thanks to the guys at Altsmoke.