I don’t have a pic available sorry, but I got the SW Daypack for my Gen 1. I was similarly bothered as to whether the flat shape would work or whether one of the more contoured bags would suit better, but it works just fine on my Gen 1.
My main priority was not having something too big, and I wanted a tank ring fit vs faffing with straps. On its non-expanded smaller setting I can fit in stuff like keys / wallet / visor spray / small cloth / choccy bar / 300ml water bottle / spare gloves / earplugs etc - just. Think I’ve only used the expanded setting once in 4 years to squeeze some sandwiches in too.
You’ve a bit of choice in fore/aft position as you have to drill the bag base yourself to fit the tank ring adapter, so that range of movement helps a lot with getting its shape to compliment the tank contour with out looking silly.