Not to us, and that's the interesting bit in this EM range.

It will be more light like than microwaves are, but less light like than light is.

And what we can learn from using that range is still new ground because it's hard to make devices that emit RF in those ranges.

Your eyes cannot see THz radiation, so no. It's invisible to the human eye. Like microwaves.

But yes, it is possible to produce a beam.

Also: to be fair, the challenge in finding efficient sources is really only one of the challenges. Not even the biggest one.