Both the Samsung Galaxy Tab S3 and iPad Pro are compatible with an active stylus pen.
I use my pen all the time, so I have tried different cases that hold the pen next to the tablet. Samsung calls their stylus the S Pen and Apple calls their stylus the Pencil. While the Apple Pencil needs to be charged, the S Pen does not require charging. The S Pen for the Tab S3 also has a built-in clip:
Pen holder that attaches to a tablet case:
Tablet case with a built-in pen holder:
Attach a pen clip and use that to attach to a tablet cover:
I sure do miss the days when stylus pens would simply fit into a built-in silo: