If you guys are flying occasionally, then it's probably better to put in a box. Also, TSA officers will inspect bikes, so they will do their best to undo your best efforts to pack and protect your bikes because they will never pack the bike properly like before. Then it goes through the Gorilla Zoo of nasty baggage handlers and then hope it doesn't get damaged. Especially with the labor dispute Air Canada is having now with the unions, people may not play nice during any labor conflicts! With my hard case, I have packing instructions with photos to help TSA officers pack my bike back properly. But at one time, they didn't pack the bike properly and bent my Kinetix Pro rear wheel paired spokes and got it out of true. Some airports do allow you to witness the TSA inspection and you may verbally assist them to repack the bike into the box or case. I never had this done, but my friends told me that they had this experience. Some airports won't.

Unlike a decade or two ago, things have changed for the worst especially after 911. As I said earlier, if you fly infrequently, a bike box is fine or even a cheap bag with lots of packing materials. If you fly frequently and bring your bike on flights two to 5 times a year, you will need a hard case just to be on the safe side. Last year's trip to Arizona, a friend of ours brought their Trek Madones (the 6 series) and one of them got damaged even boxed. Problem, it got inspected by TSA official and wasn't put back properly enough and the rear triangle got warped. Imagine you can't even stick your rear wheel and realize the frustration. Claiming bike damage is always very tricky as airlines always claim that if you don't declare it then you're liable for the damage, but if it got TSA inspected, then TSA is liable. But good luck in getting them to pay for the damage then.

Btw, even with my best efforts packing the Dahon in my hard case, TSA officials sometimes get it wrong packing it back. So far, my lattice latch assembly on the Dahon is slightly damaged (scratched and bent) I suspect of them trying to force the bike in back into the case and the rear derailleur hanger (even detached) was slightly bent. Thankfully, ThorUSA have spare parts available -- just that I haven't needed to buy them yet. I travel quite often btw.