This is a nice start, and succinct writing is a valuable skill. For a serious student of writing, the automated feedback is insufficient. Human feedback would be most useful. Designing automated feedback would be tricky, because the rewritten text must both be grammatically correct and have the same message.
FYI, There is a sentence simplification exercise inside of the larger app "Elevate Brain Training" on the Google Play app store for Android.
FYI, There is a sentence simplification exercise inside of the larger app "Elevate Brain Training" on the Google Play app store for Android.