OK, such good answers above. I am going to make a few points that maybe haven't been covered.
1. I tried the ballistic version of the Smart Alec before settling on the Halcyon. The ballistic SEEMED significantly heavier to me. This might be my brain playing tricks, but it appeared to make a difference in my personal comfort level. Logically, any weight difference should be erased when you fill up the bag, but I decided to stick to Halcyon. The other factor for me was that the ballistic version is made with some cordura parts on the exterior, and as an owner of two furry, meowing beasties, I liked that I could set the Halcyon version on the floor and know that it wouldn't pick up any lint or fur, since it is all Halcyon.
2. I don't use the Smart Alec as a personal item, but I have taken it as a carry on when I check a suitcase. It fits well under the seat in front of me, unless there are bulky AV boxes or something preventing it. This is important because the overheads get full sometimes. I like staying out of the fray and keeping everything in my seating area when needed.
3. Since my other frequent travel bag is the Aeronaut 30, I just bought some dedicated A30 cubes. They fit delightfully in the Smart Alec. You probably already saw this post, but just in case, I'm linking to it again. I'm excited to use it on my next trip, because I think it will make everything neater and easier to find. Most importantly, they will let me segregate my clothes from the stuff that I want to remain at the top of the bag.
4. I don't know if I'd call the Smart Alec "sleek", but it does have a sort of barrel shape which I find easy to deal with. If it's packed in a certain way, it stays pretty cylindrical. I have taken off the bungee cord, like @Juanito mentions, and that improves the appearance IMO. Though if it is under-packed, the bungee can be helpful.
5. One thing I'd definitely take as an accessory, as mentioned above by @ilkyway, is the Side Effect. I personally keep my passport, cards, money and phone in the SE when I am flying, and most of the time it is on a strap and arranged like a purse, so it's physically on my body rather than in the overhead or under the seat. And of course when going through security the entire SE can be zipped up securely inside the larger bag, so this works well.
Three photos:
The Smart Alec in use for a shopping expedition (I was going from work and thought the backpack would be more comfortable to walk with than a bunch of shopping bags. I had a stuffed animal, at least one board game, and a lot of other things inside.)
The Smart Alec, showing how it cinches:
A photo of the SA under a seat in a plane. I think it may have been Jet Blue? Anyway, it fit pretty well.
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