I own a desktop 3D printer. It's hard to get it calibrated (for every print you make). And I'm not even talking about Z-axis calibration (even thickness of each layer)
Even swapping filament takes ages.
Doodling sounds nice though. But items made with one of those can't be used in structural situations.
Even a simple keychain is brittle and weak (from a handheld one) since it is impossible to control the adhesion between the layers...
Also, different types of filament need different operating temperatures and they require different cooling down times etc. (or the item will warp)
5-7 years untill we see some actuall usable household 3D printers.