Using Mac Mini as portable computer?

Carrying around a Mac Mini is really no difference than a laptop with regards to damage. Not withstanding severe abuse, a rotating hard drive is likely the weak link with regard to damage due to normal jostling.

A fusion drive had a rotating hard drive paired to a solid state drive (SSD). Files used often are on the SSD for faster access.

On a laptop, the screen seems to be the week link since dropping it on a corner can damage the screen

If you are shutting it down every time you are moving it, it is perfectly fine to move it around as much as you want. The only delicate moving part, the hard drive, will not be moving and the read/write head will be parked so no problem there.

EDIT:

I should add that the only issue that may come up is with ports, USB, video etc., They may wear out prematurely with you plugging and unplugging things on a twice daily basis.

No, the ports are all the same. So if you are already doing that with a MBP then there is no difference with a Mac mini. You are going to experience similar lifespan either way.

The only reason I brought it up is that a purpose built portable computer has a built in display, keyboard and trackpad, everything you need to operate the device without having to plug anything in. Most people use it that way. A desktop class computer does not have those things so you have to, at a minimum, plug in a display. The mouse and keyboard can be wireless.

The hard drive portion of your Fusion drive is an identical drive to the ones used in laptops.

So, the drive is no more vulnerable than HDD in a laptop.