Sounds like a great way to extract what they're directing attention to and how much attention they're directing to it! What specific questions do you have about Pupil Labs eye-trackers?

I wonder if with pupil labs (pupil invisble) I can design experiments on a computer screen or only in natural and ecological environments?

I guess you could in theory, but if you're going to be bringing people into the lab for experiments where you're measuring eye movements, then you might want to opt for a remote tracker with a higher sampling rate.