Is this software developed by DesignSpark themselves?

DesignSpark Mechanical is a result of partnership between RS Components/DesignSpark and ANSYS SpaceClaim with the software package itself being developed in-house at SpaceClaim.

The feature set has been intelligently put together to give its users the perfect entry point to the vast industry of rapid prototyping and primarily 3D printing.

For users looking for more, paid add-ons for technical drawings and file formats support (STEP, IGES) are available.

https://www.rs-online.com/designspark/introducing-the-new-designspark-mechanical-add-on-modules