The first thing I do with a top handle bag is hold it by the handle alone, no shoulder strap crutch, and see how it sits against my hand for a good minute. A cheap one will dig a thin seam straight into your palm before you've even left the shop, because the handle is stiffened with something hard instead of properly padded or shaped. A good one spreads that weight along a wider curve so you can actually carry it, not just pose with it on your elbow for the five minutes it takes to walk from the car.
Where this bag falls short is obvious if you carry much. Nappies, a laptop, a change of shoes, forget it, the whole point of the shape is that it's small and self contained, so if your day needs bulk you'll be fighting the zip or leaving half your life at home. It's also not a bag for a wet Tuesday with both hands full of someone else's coat, because most only come with a short strap option at best, and some none at all. I learned that one stood at a bus stop trying to hold an umbrella, a top handle bag and a toddler's hand, and losing that battle in front of everyone.
Sizing with these is less about measurements and more about proportion against your own frame, since there's no real fit to speak of beyond whether the handle drop lets your hand through comfortably with a coat sleeve on. Try it on with whatever you'd actually be wearing, not just a t-shirt. Check how it sits against your hip when you walk, because some swing forward and knock your leg with every step, which gets old fast. The handle itself is where corners get cut, so flex it, press it, see if it's got any give or if it's rigid enough to crack with age.
Before buying, look at how the handle joins the body of the bag. Stitched and riveted properly it'll outlast the bag itself, glued on it'll start lifting within months, usually right when you're relying on it to not drop your keys down a drain. Check the lining too, cheap satin pills and snags on anything with a zip or a key ring inside, while a sturdier cotton or jacquard lining shrugs it off for years.
This one's for anyone who wants a bag that looks deliberate without trying, and who's happy to carry a smaller bag within a bag for the actual chaos of the day.