Recovery and muscle therapy products work by applying a physical input to the body: pressure, vibration, compression, heat, cold, positioning, or relaxation time. The product category sounds broad because the mechanisms are not the same.
A foam roller changes pressure through bodyweight. A massage gun adds rapid percussion. Compression boots use cyclic squeezing. Heat and cold alter sensation and local temperature. The decision should follow the mechanism and the user's context, not a promise that a tool can repair training stress on command.