This problem is in two parts both of which can affect the longevity of the tiled installation.
Size – the depth of the movement joint must match that of the tile and adhesive bed. Ideally the top of the movement joint should be slightly below that of the tiles. (1 to 2mm maximum). Under no circumstances should the movement joint be proud of the surface.
The movement joint should not be considered as a stepping stone for traffic. They are not designed accept these impacts and stress in isolation.
Typically the signs of an incorrect size would be – Too tall = impact damaged side supports. Too small = chipped tile edges.
Material – This is an example of over optimistic cost saving. Plastic Movement Joints have a very limited use in domestic and very light commercial areas. In ALL other circumstances please, please use a movement joint with metal side supports. They cost more but their performance is absolutely superior to plastic.
Metal side supports transfer movement directly to the flexible infill. Plastic supports will bend or deform.
Metal side supports provide good protection to tile edges against chipping, Plastic supports don’t!
The infill on plastic Movement Joints is prone to damage from impact and specifically from ladies high heeled shoes. The infill on metal based profiles is tougher and much less prone to this type of damage.