I take Clonidine ER which is very similar to Guanfacine for treating ADHD (blood pressure medication that is an alpha-2 adrenergic agonist). I also take stimulant-based ones on top of it during the day.

I requested Clonidine specifically to help me sleep and take it in the evenings; my dose is very sedating. It's my understanding that Guanfacine tends to be less sedating; it's not as aggressive on the c(p)ns.

Does it help with my ADHD? Yes-ish. It's calming and slows my brain and body down. My end of day crash can be pretty rough, and the Clonidine eases a lot of the mental scatteredness that I go through. If I'm stuck looking for something to watch, play, etc, it saps my brain enough and allows me to pick whatever it is I want to do to end my day. I would assume a less sedating version of what I take would be moderately effective for day time attention issues. I've seen people have success with both for their symptoms, but I've also seen it not click for people.

You will probably need to log your blood pressure for a few weeks when starting just to make sure it's not dipping you too much.