Composite materials containing hydrogenated La(Fe,Mn,Si)13 powder and 5 wt.% of polymer binder have very good magnetocaloric properties and can be machined in a heat exchanger. These heat exchangers have to fulfill certain requirements regarding their mechanical and chemical stability. In this paper, we have investigated the magnetocaloric properties of thin composite plates produced by two different methods: 1) wire saw cutting and 2) cold rolling. The flexural strength of the plates was investigated by three-point bending method. Furthermore, the corrosive behavior of the plates in different heat transfer fluids was investigated. Finally, the adiabatic temperature change and the magnetic entropy change of the plates were observed over a seven-month period in order to evaluate their applicability in a real device.