This is a twist of legislation.
On my side of the world, a Roni is just an accessory to a pistol. The pistol is still a pistol if you can install and remove the accessory without tools. A Roni or Micro Roni would be the cheapest way to try PCC if you already have a compatible pistol.
A rifle or carbine is easier to get in terms of bureacracy, here, as long as you have at least 30 cm / 12" of barrel, and it cannot be fired at a length of less than 60 cm /24".