An electric mixer is a worthwhile investment if you are a regular baker. The most important thing to check is that it has a strong motor. The motor drives the cog that drives the dough hook or paddle attachment. If you overheat the motor and it burns out, you will generally need to replace the whole mixer. This can happen if you are often mixing dough with a low water content, as the dough will be stiff and cause the motor to work extra hard to move the dough hook around. This is not worth burning out the motor for. If you see the mixer struggling, and the dough hook is stopping and starting, take the dough out and finish it by hand.