I bought the SMALL to protect an Osprey Kyte 46, the women's version of the Osprey Kestrel 48, in the case it would have to be checked on an upcoming domestic flight (I hope not!) My pack isn't overstuffed and there is more than enough room for any "extras" (trekking poles, a pair of hiking boots) I agree with some of the other reviewers in that the sling strap makes the pack awkward to carry. The pack comes past my knees and almost to my ankles when carried by the strap (I'm 5'3). I wouldn't want to carry it in the airport for any distance. I'm also not sure how much weight the strap could withstand over time. My pack only weights about 20lbs when loaded. The airporter is made with quality material and looks durable for the protection needed against baggage handlers and I like that it has the ability to accommodate a small TSA lock, (not included) but Osprey could have designed it better. It would be more carrier friendly if it had backpack shoulder straps or the ability to expose your own packs straps. It would also help if there was a daisy chain on the outside of this cover once it is folded so that it easier to clip to the pack. I used my sleeping pad straps to attach it to the bottom of my pack. It dangles a bit since there is only one small handle, but it works.There are not many options that I've found for protecting a backpack. I chose the Osprey Airporter because it was smaller and cheaper in price compared to the Sea to Summit Pack Converter. If Sea to Summit comes out with a small pack converter for packs 50L or less that would be my top choice unless, of course, Osprey redesigns theirs.