Upright toaster is very quick and low risk of burning even when left unattended. I my experience, that timed example falls apart unless you're right there to take it out of the oven. I don't drink coffee so have no reason to hang out in the kitchen. I'd start it then go to my room and get dressed and return to my toast on my own time. However, my toaster oven behaves like a real oven and holds heat even when the elements turn off, I'd have to do a lot of experimentation to figure out the right time/temp setting. Figuring out the desired setting on a upright is incredibly easy. Once set, it's set and forget. You just push the button, walk away, return when you want to eat your toast.

Toaster's smaller and easier to clean. Quicker to start, if only slightly. Probably faster. Wouldn't be surprised if they're more power efficient per slice of finished toast. Toaster oven, being large and having so much functionality overlap with a normal stove (and microwave, to some extent), is far less common (at least in the US) than the smaller and more focused toaster. Most two-slice toasters you can easily stuff in a drawer or cabinet. Toaster ovens demand permanent counter space.

Non-oven toaster is better at making toast. They do a more even job on both sides. Toaster ovens never quite get it right and bread placement is finicky, too close to the door and it often doesn't brown well especially in cheap models. I still use a toaster oven because it's more versatile but it IS worse at making toast.

Takes up way less space!

Has way less utility! Jk, this is a valid point, I just happen to have plenty of space so this isn't a factor for me