The Osprey Metron has now been in use for about a month on my daily commutes. The bag has held up really well under the stresses of a full load. The load includes a MacBook Pro 15″, a camera, a notebook, bike tools and tubes, an extra pair of shoes, a jacket, and a host of other things. It regularly carries between 20 and 30 pounds, and does so effortlessly. My back is none the wiser about how much I have in the bag. It is super comfortable and incredibly well designed. The compartments make sense and are easy to learn. The computer is completely cushioned, and the helmet strap is brilliant. The attachment point for the blinky light is also well thought out; when riding, it is perfectly visible to the vehicles and other cyclists behind you. The bag market is quite competitive, but I think Osprey is well in the lead with the Metron.
Do you use the 25 or 35 with the macbook?
I use the 35 as I tend to carry a large load. It will easily hold a 15″ MacBook Pro, a pair of shoes, and all the other necessary everyday items.