I am currently installing similar lights in my house. Ceilings are just under 8'. So far, have installed them in the living room, kitchen and dining room. All on dimmers. Got them in 4-packs at Menards, they are 800 lumens each. Got a 2-pack, did not notice they were 1000 lumens. Can't tell a lot of difference, but placed them where the difference won't matter.
As others have said, how you plan to use your barn space will determine whether they will be adequate. For general lighting, they will probably be just fine. If you are going to be doing some carpentry or machine work, you will also want some task-specific lighting.
Installation is easy. I initially considered one of those hole cutters that has a scribe on an adjustable beam, but they are horrible to use. My son got a 6" hole saw from Amazon. It works GREAT. Just measure out where you want the light, put the pilot drill on the mark, TURN ON THE VACUUM, start drilling. Using a shop-vac really tames the dust.
.