It's not, it's just a different approach. Deformer masquerades as a regular everyday item, Mangle is made to never be seen. The tyles of things that they bend are virtually identical, but the devices are very different.
So, if you do not use a Sharpie in your performances you should check out Mangle. If you do use a Sharpie during your metal bending routines you may prefer the Deformer.