I have been using the kettlestacks since January and have found them to be very easy to assemble, use and it does almost everything a regular kettlebell does.
Since the plates are adjustable you can also set them lower than the cast KBs without hurting the forearms of beginner Kettlestackers.
I highly recommend them for their functionality. It's a great product.
I'm going to look into making base plates that can be attached to the main bolt so that renegade rows can also be done with them.