A little pricey perhaps...
...but it worked brilliantly. I had a defective TRV to change and didn't want to drain the system with the attendant cost of replenishing the Fernox additive. For about the same price I saved the bother of the drain down and now have the tools to allow me to do the same job over and over, as needed.
With the feed pipe bunged off I took the opportunity to fit a serviceman valve so only need to bung the overflow pipe next time. I also fitted a new AAV while the system was 'suspended' and no drips whatsoever. There was a slight loss of water, about a teacupful, as I swapped out the rad tail for the new valve but considering I didn't drain the radiator as the instructions say you should, I was well pleased.
Excellent bit of kit if a little pricey.
Verified purchase: YesCondition: New