A pot magnet is embedded in a steel pot. The steel pot increases the adhesive force of the magnet on direct contact with a thick iron surface. If there is no direct contact with the counterpart, or if the steel plate is thin, painted, or rough, you can strain it much less.
The indicated adhesive force was measured perpendicular to the surface to which the cup magnet should stick. It takes a lot less strength to move the magnet sideways. Therefore, you can strain a pot magnet much less if you use it on a wall as opposed to using it on the ceiling.
Neodymium cup magnets are not rust-proof and therefore intended for dry indoor use.
Maximum working temperature:
Most mounting magnets can be heated to a temperature of up to 80°C without losing their magnetization (ferrite magnets and certain CSN-types even higher). The adhesive that connects the magnet and the steel pot may become brittle at continuous heating to this temperature. Hence, it is recommended to use pot magnets only at room temperature.