MotionFX is part of the X-CUBE-MEMS1 software package, for which you can also find the software licence agreement on its website. There you will also find a restriction:
You acknowledge and agree that any use, adaptation, translation or transcription of the Licensed Software or any portion or derivative thereof, for use with (i) product that does not include ST Device and/or (ii) with device, having similar functionalities to ST Devices, manufactured by or for an entity other than ST, is a material breach of this Agreement and requires a separate license from ST.
Further applies (and was previously mentioned in the SLA):
ST Device: means the combination of at least: a) one ST microcontroller and b) one device chosen by You between a ST radio frequency connectivity device and a ST MEMS sensor integrated circuit; a) and b) manufactured and sold by or for ST.
So if you use an STMicroelectronics sensor but the software does not run on an STMicroelectronics MCU, you are in breach of the licence agreement.
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Good luck!
/Peter