Picked up this vaphit x stem the other week.
It has glass beads inside to try and cool things down, also has a little star shaped ruby at the front so the vapor path/airflow doesn't get clogged.
It's ok, doesn't cool anywhere near as much as the native stem does, but it does cool things a little, I can't do as many back to back bowls with it.
It's handy for when my stems are soaking.
It's heavy, satisfyingly heavy... In fact as much as I really prefer lighter stems, the weight of it is my favourite thing.
Weight comes in at 86.56g, while the native tempest is 33.47g.
Got it direct so it was only about £17 Inc postage, for the price it's quite good I think