Radiator Automatic Air Bleed valves.

[wetdrip]

5 Pack of Radiator Auto Bleed Valves - Automatically Bleeds Your Radiator To Keep It Working Well: Amazon.co.uk: DIY & Tools

Any thought on these or like products?

 

[Chalked]

I don't like them. Tend to leak after a few years.

It's curing symptoms, not the cause.