Not sure about that "weak to magnets" warning.
Controller being this product?
https://www.newegg.com/corsair-cl-9011110-ww-black/p/N82E16811978004#
And those 2 sticky pads are possibly rubberized/flexible magnets - correct?
With adhesive on one side to stick to the controller and the other side being "magnetic" to cling to the metal wall.
The User Guide though refers to the pads as "Mounting tape" (see Page 3) and Installation Step 2 (Page 7) uses "double sided tape.
https://www.corsair.com/corsairmedia/sys_master/productcontent/CommanderPRO_Install_Guide.pdf
Either way, the sticky pads are likely to be as cheaply made as possible and likely to degrade with time and heat exposure.
Mount the controller as you desire but keep an eye on it. Likely to end up dangling sooner or later.
Consider mounting the controller using
Velcro tape. One strip on the mounting surface, the other on the controller.
You will likely only need a couple of small pieces - about the size of the sticky pads that came with the controller.
Should make it easier to remove the controller if that becomes necessary.
Just my thoughts on the matter.