I really dislike USB charging generally. I have a few mods where that is the only option, and with an internal battery mod, that really is the only option. I use magnetic usb chargers to help cut down on wear and tear, but really, besides safety issues and wear on the port (which are truly THE MAIN) reasons to buy an external charger, I love the convenience of just swapping batteries out. The charger doesn't have to be insanely expensive, I got a nitecore intellecharger 2 bay, and it has worked out well for me. Also, getting another set of batteries will allow you to just swap out batteries as needed, not wait around for them to charge or vape passthrough (if that's even possible for the mod you get) as IMO passthrough vaping is just putting MORE strain on the mod and batteries by asking it to switch between charge-discharge every time you take a puff.
Just my humble opinion as always, but external battery mods, most of them, aren't really "meant' for USB charging. Some of them can DO it, but as stated above, the issues involved can cause early mod death or battery death (mostly, the USB port is used for updates and etc. or just in a total pinch) as a secondary (and not really advised) way to charge.
Best of luck,
Anna