Has anyone installed one themselves or had one installed? Have you been happy?

I'm looking to take the edge off in my insulated attached two-car garage/workshop (~600 sqft), and have seen some attractive prices on the units themselves. Trying to keep it above 50 in winter, and below 80 in summer. It currently gets to maybe 35 in winter and 95 in summer.

I would rate myself as "pretty handy" (have swapped electrical outlets, installed lights, done some soldering, a little drywall), but I'm a little intimidated by the electrical and the coolant aspect.

Is this something where I could do most of the work, and have someone do the tough stuff?

Any recommendations for brands, sizing, contractors, or any gotcha factors?