Before the Metro Sling Max, I was already using the Vertex Pouch as my everyday bag. At first I was impressed, but I eventually found the Vertex too compartmentalized, that there was no "big area" for some items that I can drop in easily. So I gambled on the Metro Sling Max, even though it's shy of 0.5L in capacity (as it's stated in the info page). However, to my surprise, I was able to pack the same amount from my Vertex to the Metro Sling Max, and then some more.
The compartmentalization is balanced out with a large and tall cavernous space. So it's perfect for an OC person like me who likes the inline pockets and spaces, yet at the same time, I have extra space for my "drop-in" items such as a phone, wallet, etc.
The other feature that I love so much that the other sling bags don't have are the side webbings. I can easily attach my keys, carabiner + water bottle, etc. I even took a step further and acquired for myself modular bags and attached on each side. The bag can now hold my umbrella / water bottle + auxiliary items for EDC (see picture).
Thanks Alpaka!