You asked one hell of a question. I'm not sure I can give you a simple answer. I apologize in advance for my lack of brevity.
Both of those mods have a .3-ohm minimum, so they will not fire a .25-ohm coil. I'm not sure what the actual continuous discharge limit of the internal batteries are, but I'm assuming they are designed not to let you run them past it.
The "Max Current" spec on those devices refers to the maximum output current, not the maximum current it can pull from the battery. There's a big difference there, which I will get into a bit later. The main thing to know here is that you needn't worry about it on devices with built-in batteries. They are designed and configured to run within the limitations of the battery.
When we talk about current in terms of safety, we are referring to the max continuous discharge rate of the batteries. This only comes into play with devices that have removable batteries, regulated or not. That's when you need to be aware of the CDR of your batteries and check to make sure that your device isn't exceeding that number.
Use steam engine. It really covers everything. Now, for some stuff you don't need to know yet but should know anyway if you wish to take things further...
...for unregulated devices, coil resistance is everything when it comes to performance and safety. The voltage is fixed at whatever the battery naturally puts out, so the amount of current and thus wattage always depends on the resistance of the coil.
Because you're running straight off of the battery, there's nothing stopping you from building a coil that can pop a battery, as the battery will give as much current as the coil will pull from it, even if it shouldn't. A dead short in the atty or within the device itself will vent a battery. It is also possible to drain a battery too low, which can cause your batteries to vent and catch fire when you charge them.
When you read about vaping devices exploding, a mechanical mod and an ill-informed user are usually involved. They are not newbie-friendly and require a lot of knowledge and experience to use properly. They do not have safety nets. You need to be up on your ohm's law, always use an ohmmeter, be able to recognize a short BEFORE firing it, and have a good grasp of what your batteries can and cannot handle, as well as the ability to recognize the signs of an over-stressed/over-discharged battery.
Regulated devices generally do not care about ohms. There's no resistance involved in how one gets its power. The battery drain is dictated by the wattage setting. If you set it at 100w, then it will pull as much current as it needs to hit that at the batteries' voltage under load.
So, if you build a stupid-low, .1 coil that pulls 38 amps at 150w, that doesn't mean it will take 38 amps from your battery (which is far more than any battery on the market can handle, btw.) If you're running a dual battery box (something like the Sigelei 150w,) then it will pull 20 amps from your batteries, as that is all that is needed to achieve 150w with fresh batteries kicking at 8.4v. It uses something called a buck converter, which trades the excess voltage coming from the batteries for current.
This, along with their many built-in protection features, makes these types of devices much safer and more power-efficient. What unregulated devices do with current, they can do with voltage. The more current that is needed from the batteries, the more taxed they are, and the higher the likelihood of catastrophic failure is.
The only trade-off is that unlike mechs, which pull a declining amount of current as the batteries are depleted, VW devices need to pull more current from your batteries as they deplete and their natural voltage drops. This is where you need to be careful. What is a safe wattage for fresh batteries may not be so safe on half-dead ones.
I'm oversimplifying it a bit, as there are parallel regulated boxes which use boost circuitry to hit higher wattages, but those are uncommon. You will be much more likely to encounter single or dual-series boxes that work as I described.
