It's not too uncommon. Pan Am 103 was brought down by a bomb built into a portable tape player, for example. Electronics are a good place to hide bombs because the complex internal structure makes it hard to notice explosives when they're x-rayed. This is why you have to send laptops through the x-ray machine separately and why they'll sometimes ask you to turn it on to prove that it works (so you can't hollow it out completely and just use the case for your bomb).

You'd have other options, but nothing that large. Size does matter. Pan Am 103 is about as small as a bomb can possibly be and still destroy the airplane, and even that was only possible because of an extremely unlucky placement of the bomb within the cargo hold.

In 2010, two bombs concealed in laser printer cartridges were found in freight planes.

https://en.wikipedia.org/wiki/Cargo_planes_bomb_plot

Presumably, someone who doesn't want to carry big, round, black bombs with a fuse sticking out of the top, with the text "BOMB" painted on the side.

There really aren't a huge number of options left for concealing a small amount of explosives, given the current restrictions on pretty much everything we take onto airplanes.

I always wondered: what is the point of taking laptops out of your bag and putting them in a separate tray?