i picked up a replacement for a 99 civic, from canadian tire. ($40)
It looks identical to the factory one, it actually screws
into the engine block.  I could imagine some different styles
causing problems, there is the kind that just sits in the
expansion plug, and you tighten a bolt to expand the base
of the block heater.  I couldn't imagine this style of
block heater being very secure, but the screw in type has
got to be pretty fool proof.  I wouldn't hesitate to go aftermarket
on the screw in type.

But trying to get that puppy loose was another story.  They
use some kind of thread locker on the threads, so its
very difficult.

t