Welcome!
Are you referring to the topper or the box
mod itself?
Don't have either box
mod, but I have both toppers. To me, no difference - the Mini just holds more than the Nano.
As far as the mod itself - the Nano is a slightly smaller form factor, I believe. Comes in purple or pink as well as in black. The Mini looks like it can come in blue, black or white.
Also, there are some variations of the Mini - they can go upwards of 200W. Just depends on how you want to use it.