Honestly, that still sounds like a minor inconvenience compared to DIY. Those things seem pretty set-and-forget beyond filter replacements.

There are aesthetic concerns, it’s harder to have a bunch of air purifiers spread around your home if they’re ugly as sin.

Having one very powerful air purifier hidden away in another room is not as good as having a bunch of smaller ones spread around.

Not exactly, price increases with some certifications and branding. In the high end of purifiers, they can handle much smaller particulates and gasses (e.g. carbon matter measured by dozens of lbs with replacement filters costing hundreds). The most effective filters for general use will have higher CFM. CFM also decreases with smaller particulate filtering. Unless you're spending ~$1k+, most activated be carbon seems to wear out faster than it's worth considering.

Overall, yes, a cheap box filter (placed specifically in the bedroom, if limited to one room) is often the most effective.