I know almost nothing from electronics.
But I see things and I can understand some.
For example, my Luxe mod is able to charge at 2.5A if I remember well, its the spec for the Omniboard 4 chipset.
There are differences when using different power adapters. time ago, I got this data:
With 1A 5V USB:
-avarage charge time from "0%": 260min.
-measured batts. temp at 50% charge: 25ºC (with batt door closed) @21ºC ambient
-avarage batt. use after, typical daily use: 36h.
With 2.5-3A 5/5.25V USB:
-avarage charge time from "0%": 120min.
-measured batt. temp at 50% charge: 44ºC (with batt. door open!) @21ºC ambient
-avarage batt. use after, typical daily use: 20h.
So high temp is the main reason I almost never, since I have the mod, charge it with fast charge. I cant trust batteries charging near to 50ºC, but at half that temperature? not a problem for me.
External battery chargers could stress batteries as well if the power output is high, so for me theres no difference.
Im I damaging the USB port or the PCB of the mod? I think if the USB port were just for firmware upgrade, Vaporesso would put it clearly in the manual. The port will wear just like any other such smartphones. Having care and being precise when connecting its a must if you want to conserve it. If you are a butterfingers, its your problem.
Do the mod electronics suffer when charging somehow? I dont know. I would say its not likely. At least not this chipset. Im charging it for almost 2 years now and it works like the first day, but the 2xVTC5A now seems to last a little bit less (time to replace, possibly).
Please, dont take what I say further than a bar counter conversation.