At the last minute, I decided to take the Peak Design Travel Backpack 30L on my trip to Japan. I had been using the Tom Bihn Synik 30 for a while, but I wanted to try something new. The Peak Design bag is a bit smaller and more compact, which I thought would be better for traveling. I also didn't end up packing my clothes in the Peak Design bag, but I did use it for my tech gear. It was pretty heavy when loaded up, just about fitting what I needed and weighing in at 11kg.
I didn't love the Peak Design bag as much as I thought I would. It doesn't have the same level of organization as the Synik. I found myself digging around for things more often than I would have liked. There's only 1 external pocket, and it's not all that big, so it's hard to stash stuff that you want to grab quickly. The full clamshell opening is convenient, but it can be annoying if you want to get into the bag quickly, or without taking it off. The straps aren't bad, but they don't feel as comfortable as the Synik's and the strap adjusters weren't very secure. There were quite a few times I'd put the bag on and have to re-adjust the length of one or both straps. The back panel is also a bit less breathable, which made it a little sweaty on hot days. I think the bag is great for short trips, but I wouldn't want to use it for anything longer than a week, and probably not anywhere hot and humid.
When I needed it, the expansion was actually really nice. I was able to fit a few extra things in there, and it didn't feel like the bag was going to burst at the seams. The side pockets are also a nice touch, but they don't hold much, and if the bag is really packed out then it can be a struggle to get a water bottle in and out. The ability to strap a jacket to the outside of the bag is a nice feature, and I used it quite a few times. I think that the Peak Design bag is actually a good duffle bag, but not a great backpack. If I was just travelling by car I think this would be a really good option, but for a trip like this I think the Synik or CTB would have been a better choice.