Slitherine

Is it useful to have more then one labs by search area. what's the research speed increase between one or 2 labs?
what's focus impact?

From what i have gathered the difference is not that great

Focus makes it 1 turn faster unless there's only 1 turn to go anyway in which case it doesn't do anything.

Is it useful to have more then one labs by search area

Yes, but there are diminishing returns. You don't double your research speed by doubling your labs.

Focus makes it 1 turn faster

Not always. It reduces the speed of all techs other than the one being focussed on, and the speed is transferred to the focussed tech. In effect you're accelerating the development of a specific tech at the expense of the others.