As above, to be used as an mtb. What would the effect be?

Don’t know about 10/11 speed but 9 works just fine and I find a better choice of ratios in road cassettes than mtb

closer ratios, not as much range. If you intend on riding up any hills keep to an mtb cassette

As above, closer ratios & not as much range.
Back when I was doing more downhill it was common to use a roadie block along with a short cage road mech.

My cycle to work bike has a road cassette and changing gear doesn’t make a massive difference to be honest, not that it matters for me on the road, even on an mtb 26 er with a 36t front chainring

I run a 10sp 11-25 on the 4x bike

as Chris said.

Shifting’ll be smoother on the road. You might miss the big rings when going up hills. I always used to use road cassettes when at uni (Sussex) and didn’t need the dinner-plate sizes