Would we be able to understand and utilize it? Would it even be
compatible for our species and society?

I would expect technology to be much further along than it is now if
we did have alien tech, assuming the above criteria were met.

If someone had the power that would go along with alien tech such as
a weapon system or energy source, I am hard pressed to imagine that
they would be able to keep from wanting to use such devices for their
own gain. Most humans are lousy at keep secrets, especially the
juicy ones.

But if such things are being suppressed and regular scientists are not
able to get their hands on alien tech, then they may as well not exist.

You should read the SF story Roadside Picnic, which is online here:

http://en.wikipedia.org/wiki/Roadside_Picnic