“The stacking header allows you to “stack” multiple hats on top of a Pi, or if you use the stacking header on a Pi Zero, you can use it has a plug-in compute module and still plug a HAT into it.”
“Cheap and handy addition for access to pins in low profile case, but most useful in a higher sided case as access is more difficult without, but you need to cut out the top if using a PiDrive case from WD.”
“A good product delivered in good time as promised. One point to note is that if you use the stacking headers in place of original supplied headers with pi HATs, then the spacing betwen the boards increases slightly and the original spacing posts will have to be replaced by longer ones.”
“Great product for use with the Ryanteck Debug Clip when your Raspberry Pi is housed in a case making it harder to plug the Debug Clip onto the GPIO, still leaving plenty of room for plugging on HATs.”