Last summer we put 4 in a large (16'x23' or so) under-eave room that had small west-facing window, so was bright only on sunny days between 3pm & 5pm or so...
We bought the brand that Lowes carries (Velux, I think) - they are less spendy than the Solar Tubes but don't have as many permutations. We also got the light kits, as this very large room had no pre-existing light fixtures (must have used lamps). I think the basic unit comes with the 'lenses' included (the plastic shields that make the unit look like a light fixture whether you have the light kit or not). We also got the extension tubes - if you get multiple units, measure and cut carefully, we only needed the material from 3 extensions to reach for all 4 of our units.
We are very happy with the tubes. They are designed for retrofits and fit between existing ceiling joists and roof rafters (if those are the right terms for the structural wood lurking in your attic). On bright days or really dim days the light is pretty even from all 4 tubes. On medium-overcast days you can tell the difference between the 2 tubes on the south side of the roof ridge (bright) and the 2 on the north side (not as bright). We have noticed no particular draft or leak issues, although they are in place less than a year so stay tuned for someone with an older install to report.
If you do get a light kit you will want to be aware of the light switch when you leave the room, it is very easy to turn the lights on, have the sun come out, not realize the lights are on and leave them on when you leave the room. When the sun is shining you can barely tell if the lights are on or not.