They're slow, (comparatively) unreliable and small. Because they're on the board a bad one means a new mobo which is generally not cost effective so it's done. I hate them and the cheap shitty hardware that they come with.

I'd like to point out that these came before Chromebooks but Chromebooks are also using them because they use the same shitty hardware as the cheapest Windows devices.

The devil is in the details, as with other kinds of SSD.