The folks at Go Fast Camper make a really great tent topper. I've done a few outings with it and am very happy with the long term lifestyle investment. As long as you have a relatively level parking spot (to avoid slipping while sleeping), it's such a luxury to be able to camp anywhere without tent setup or ground tent requirements. Also nice to be able to stand straight up inside the carpeted (BedRug) bed to change or stretch or just avoid the elements. The three locking panels seem solid (they're just aluminum, but fully hinged and the key locks work well), and the anchoring system is done with burly steel anchors (not the crappy aluminum anchors typically used on fiberglass toppers).
It easily sleeps a couple, or one parent + child. If weather was really bad, four could huddle in the tent top but couldn't lay down. If we had to, we could sleep parents in the tent and kids downstairs in the carpeted bed.
As for MPG... my stock vehicle got 28-34 (varies widely with conditions). After the 1-3/4" lift and 32" tires, more like 26-32. With the GFC on top... basically 24 MPG (highway) but can still do 28+ on clear roads, no wind, at 60'ish mph. YMMV.
A couple caveats - The stubby antenna doesn't receive radio as well as stock. I can still get the Denver public radio station nearly as good as before, but neighboring city (e.g. Fort Collins) radio reception has become weak. Also, if you use satellite radio (I do not), the camper blocks antenna line of sight. One other thing - GFC seems to use the same setup for Colorado, Tacoma, etc. The topper is too close to my CHMSL, and so it taps the brake light (as the bed/frame flexes) when I go over bumps and sometimes road joints. Although it doesn't bother me much, I wonder if a CHMSL delete (perhaps with 3D-printed cover plate) could be a solution (but unsure if OBD would sense a missing light circuit?).