If you're holding one up and wondering whether it's worth it, the question to ask isn't how it looks on the hook, it's whether the zip runs smoothly when the bag's actually full. Stand there and do that test before anything else, stuff it with a purse and keys and a phone and drag the zip across. A good one glides. A bad one catches on the lining and you'll be fighting it every single day, usually at a till queue with someone behind you.
A zip bag works hard, which is exactly why it clashes with anything flimsy underneath it, a slouchy unstructured tote with a zip top just fights itself, the shape collapses and the zip pulls at an angle instead of sitting flat. What separates the ones worth having from the ones that end up at the bottom of a cupboard comes down to a handful of things you can check with your hands, not just your eyes. The zip pull itself should feel solid, not like it'll snap off if you tug it while rushing for a bus. The tape the zip is sewn into matters more than people expect, a cheap one frays at the ends within a season and then the zip stops closing properly no matter how careful you are. The lining should be stitched in, not glued, because glued linings bubble and peel after a hot summer in a bag left in a car or by a radiator. And the stitching around the zip edge should be close and even, any gaps there are where the fabric starts to pull away from the teeth.
Where it's the wrong choice is anything you need to get into one handed, in a hurry, like a phone you're constantly checking or a card you tap with twenty times a day, a zip adds a fiddly second every time and that adds up to real irritation over weeks. For that, a bag with an open top or a clip is just kinder to your own patience. A zip bag earns its place for the opposite situation, when you want things to stay put, on a commute, in a crowd, travelling, anywhere you'd rather not glance down and wonder if your purse fell out somewhere between the last two stops. If you've never owned one, start with a plain cross body in a mid size, structured enough to hold its shape empty, with a single smooth zip rather than two competing ones, because every extra zip is another thing that can jam or break.
Once you've got one, keep the zip itself lightly waxed or just rub a stub of candle along the teeth if it starts to stick, it saves you years.