Memory expansion

Hardware and Accessories

I'm interested in some form of memory expansion for my iPhone. I've seen a couple of options: a Lightning/USB flash drive and a Lightning/USB SD card reader. There are several brands of each. Each brand seems to have an associated app for accessing the external memory. Frankly, I'm overwhelmed by the choices.

I'd appreciate any thoughts or suggestions regarding these devices and their associated apps. Which apps are accessible and which are not? Can these devices be accessed by apps other than their specific branded app? e.g., FileBrowser?

The SD card reader option seems like a better choice because they tend to be considerably less expensive (less than $20) and one can swap out SD cards for virtually unlimited expansion. Are there better considerations for choosing the flash drive alternative?

Please help me figure this out. Thanks.