EC Lync System Carry-on ultra-light and durable luggage/backpack by Eagle Creek has the unique ability of changing from a carry-on suitcase with wheels and a pull out handle to a large day pack. Its actually the exact same bag either way (it doesn't fold out or anything) it just has a removable frame with wheels.
I really liked the idea of it – it could be the perfect bag for those cheap airlines where they only let you have one bag and no 'personal item', purse or backpack. I end up on those airlines a lot, so I thought it may work well for me. In practice, though, its more cumbersome than I imagined and not especially intuitive.
It comes in a stow bag with ikea-style picture instructions. It doesn't take long to put the frame together and that's a one-time job anyways – I don't see any reason you'd want to take it apart again unless you had very limited storage space and wanted to fit it all back in the stow bag again. After the frame is together you slide the backpack over it and attach it with some clips. Theoretically, I thought this would be the easy part, but this is where it actually got tough. The clips are very tight and the straps that fit around the frame are very short and not adjustable so you're working in a very small area trying to get the tiny straps around the metal and back into the clips which are hard to press together (and almost impossible to take apart – but we'll get to that later). If the straps were just fastened with velcro the whole process would be infinitely easier and you could probably go from backpack to luggage within a minute or two, but given the way it is designed it took me 11 mins to put together the first time, which I thought was rather long, so I actually took it all apart again and put it in the bag and asked my husband to do it. It took him 23 mins!
The bag itself has three zippered compartments – a main one for clothes and most everything else with a couple of small zippered pockets in it, a large but thin pocket perfect for a laptop or tablet, and a smaller pocket at the top for accessories. It also has a stuff sack on the outside. There are compression straps and a sternum strap, but no hip strap. It also has removable shoulder straps, though you don't really need to remove them to make it into a suitcase (you can still pull up the handle), just undo the simple clips at the bottom and slide them into the pocket at the back made for that purpose.
The real problem was removing the frame to go back into a day pack. When you finally get the aforementioned clips attached, they're in there so good that I tried for over 10 mins to get them apart and couldn't. I didn't want to resort to using tools because in a hotel room you wont have access to much, so to keep it realistic I just used the side of a ballpoint pen (which I'd usually have with me) to help press in those clips, no dice. Eventually, I needed to go get the pliers to remove the clips! With the pliers it only took me 1:45 mins to return it to a backpack, but unless you carry a multi-tool with you on your trips I'd definitely try this bag out first in the store to see if you can realistically use it the way its meant to be used (or wait until they come out with a new version with velcro attachments – or at least adjustable straps and looser clips!).
Eagle Creek does have a “No Matter What” warranty on all their products so it sounds like you should be able to use that to exchange it if its not working out. Its also a great selling point for any of their other bags. To see their whole line of products, click here: http://www.eaglecreek.com/.