I have a mono Keepall 50 and used it thrice to travel overseas since I bought it last August 2010. I love the bag, definitely. But during my first trip, I have packed a lot and it did tend to be really heavy. As in. So during my second and (especially) third trip, I thought over carefully over the things I really need to carry and I survived the transfer, walking , running, etc. Well my trips don't usually last more than a week and I just hand-carry my Keepall, and carry a smaller on-the-go bag. I don't check-in. Also depending on the place you are going to, for the three airports, I had no problem with Kota Kinabalu because it was small and lesser chance of carrying the bag than on a trolley; but it was another issue for HK and especially Seoul (rushing towards the Seoul subway system without an escalator!), but the trolleys are everywhere once you are in the airport.
But honestly, for my next trip, especially if I were to go on a colder season (i.e. autumn)/longer stays, I might be still bringing my Keepall IF ONLY I have a roll-on luggage with me because I would be packing a lot due to the temperature/duration of travel. But for hotter seasons and shorter stays, I might stick with just a Keepall. Again, it depends on how much you usually pack with you --- you might be out just for the weekend but carry a lot, then I suggest you get a roll on luggage. I usually get bigger arms after I travel. Lugging a bag is my weight training. LOL