What's the deal with cutting the firewall for new fuse panels?

[71CHEVYSHORTBED402]

I'm looking at new wiring from perhaps M&H or American Auto wire.......Thing is, I saw a video on American Auto wire's "Classic" I think it's called, and them dudes had to cut the firewall.....What the?

That leaves me pondering what happens if it's a piece of junk, or someday perhaps when I'm long gone, it needs to be replaced. And there's yet another reason to cut the firewall or worse weld it up for a smaller cut. Yeah I might be paranoid. Doesn't bode well for a restoration.

I saw their fuse boxes use plastic fuses as well. Bummer..Ha!.....Alright so they're more convenient, but still.

Any input appreciated.