Firstly - they are a prick to use.
Many coils do not have the mounting slot pressed properly into them - meaning you have to force the coils onto the stakes - usually bending the "mounting spike" on the holder.
The design of the stake holders, makes it hard to pick up the coil and stake, and either place them somewhere or move them from room to room.
If you stick the coil and stake on a plate to catch all the ash, they have a real tendenncy to tip over when you do move them.
That said, I got sick of the "bottom dollar" bullshit design, and came up with a permanent solution to the holding, use and transportation of mosquito coils.