I moved from a Kahr CW380 to a P365. From that frame of reference it's funny to hear of the 365 being 'tiny' when its the next size bigger in barrel, grip, and weight. Calling it a pocket carry gun is, to me, not going to happen as the Kahr was already too big. For that, the LCP was on the bulky size and why I quit it.
It really depends on how someone will carry it in it's primary holster and location, and considering that we fall back to our most familiar use of a firearm when under stress, moving it around only adds to confusion about where it might be when you need it. Pick your spot and stick with it, then size the grip module to what you consider important. I carry my Nitron in an athletic running shoulder holster, it's not a fast draw, and size is important. At what some consider shooting distances, tho, the grip or lack of it doesn't matter much, especially if you are point or flash sight picture shooting. Most shoot far too low. SIG sights are not what some think, their own webpage states they are front sight over the target, not floating under it. Hence why so many can't get it to sight in - they aren't holding high enough. Guys my age were taught to put the bull on top of the sight blade, but now with a front dot, it's changed. And nobody gave me any memo on it, I found out recently after I got the 365.
As for the amount of carry ammo it's also interesting to hear about moving up from a 6 to 10 shot pistol yet buyers want even more with another 2 rounds.And you can, the advantage already exists, however, two ten shot mags mean 20 rounds with one mag change, a 6 round mag would require two mag changes and you still only had 18 rounds. One less mag change in a dynamic situation is a good thing as you aren't down as long getting them swapped out with no ability right then to pull the trigger. Your weapon remains functional longer.
As for carrying that extra mag, if you go to the larger reload, then you also have to consider it's a double stack, where are you going to hang it, and will the mag carrier remain appropriately concealed ie sit low enough without sticking down too far. With more ammo capacity as a plus, this is the offsetting oops, you have a bigger mag to conceal and carry.
I considered it and 20 rounds with two mags was a leg up over 12 round in two mags. Eight more bullets was good - keeping in mind that best is the enemy of good. Best is 18 round mags with a reload, nope, my Canik is not a CCW.
Yes, the SIG FCU concept of a drop out trigger group is different. Can you change parts out easily, yes. Should you take out the FCU to clean it, no, SIG says don't, and if you do, expect that when the grip unit is no longer there to keep the parts in their correct relationship, which is required just the same as a framed handgun, that things will jostle loose. You then learn the error of your ways and also how to put it back together, which is no more difficult that assembling an AR trigger in the lower. By knowing that, you also can do it yourself rather than 2 weeks at SIG waiting to put it back together for you because SIG told you not to in the first place. SIG was actually being nice about it. Blaming SIG isn't.
Can you swap grips, mags slides and barrels, yes. And that is why the P365 is selling like hotcakes, while other makers are still using the previous generation technology with fixed serial number frames than can't be changed out, require gunsmith level knowledge to work on them, and force you to buy another gun, and another gun to get the size, capacity, and sights you find you can use. You can even add a safety, I did, and it's standard not custom work to put it in if you so desire. Very few other guns offer that or even the choice. Another plus for the FCU and grip, it's easy to install the safety with a small notch to give it working room, or buy a grip frame in the length and color you want. Yes, you get to have the color you want now, not what that model alone offers. Those days of 12 custom P938s are waning, they are currently only offering 3 models as the P365 closes the door on those older designs. Hint: if you like them, collect them now as things loosen up. I sold mine to get more capacity and the ability to work on it myself.
I got the P365 I wanted, stuck with the small frame and slide, added a left side safety, may even add more SAS features. As a concealed carrier, extended mag buttons, sights and stuff all sticking out are just more snag hazards for carry - others make it their target gun for the range and enjoy it. Some swap parts from one to the other and get both. It's your choice, not set in stone and certainly not something someone else has to do for you. A line assembler making wages put it together, we can certainly learn how to do the same for ourself.