I adore the Boost Air, but only if you need an inexpensive option or have a three-across that makes buckling hard. It's very comfy for small and large kids alike. But the quality is definitely all Dorel (flimsy headrest, kind of snaggy mesh covering...you get what you pay for).
I'd leave the headrest on, honestly with a booster it's not an issue if there's no interference. (it's the same as your head being there, you wouldn't take it off for a person sitting there, there's no top tether or installation tightness issue with most boosters, either. There's some evidence that even boosters that don't require headrests do little to prevent whiplash, so headrests are probably beneficial for kids in boosters).
I'm holding out for a Kiddy Cruiserfix, myself. If it really comes out in May, that's only 6 weeks, get a footrest for leg support in the meantime (all my kids have needed small light plastic stepstools once their legs are too long and their backs start hurting in boosters).