True, and I've seen people using copper pipe, but I don't personally like the idea of smooth pipes, seems like a water disaster waiting to happen when the tube slides off, reamed out brass barbs like the block in the image do the job well enough
I recently got this block from NZ made by a guy
Tojja and have modded it a little.
This is what I've done:-
Probably about an hours worth of finishing, (while watching TV), required to get it that shiny/ round the corners etc. Then the clear lacquer took maybe 10 min to do and over night on the room central heating rad to harden. This then needed T-cut & polish, about 15mins The barbs which are my own brass ones bought locally and drilled out from 8.3mm ID to 10mm ID (going up in incremental drill sizes). They are tapered barbs so I had to force them in so they cut a larger slightly wider thread, but the thread was the same 1/4 bsp. Once they would go in to the end of the thread I cut the extra length off and used a taper cone drill bit to shape flow all the ends smooth.
I also centre punched the area inside the block below the input channel to increase surface area & turbulence. Barbs were then screwed in with a small amount of Araldite on the threads and it's ready. So total work probably 2 to 2½ hours.