It fits up to a 16 MacBook Pro, which is perfect for most professionals
These are not allowed for other species, and be sure to read up on the rules
Incidentally, K-TEN Blue Ocean BKF175R2 is a floating plug, but the weight of the hook makes it suspend and slow sinking
Enhancements I would make if I were to go down the custom packbag route, would be to add a couple more side pockets lower down like the Serac Expedition has, replace two of the upper side pockets with a long pocket, like the Tioga has but probably on both sides, add an extension sleeve with drawcord to the top like the Tioga has, use buckles and webbing rather than cords and cordlocks for the main lid, and adding strap attachment points to the top of the lid as the Tioga has
The larger 45g model in black/chrome or blue sardine have been my most successful and when used in low wind conditions