How to check for a worn chain:
Whereas this tool is more basic and the 75% feeler doesn't quite slot between the chain teeth indicating the chain doesn't need replacing yet.
I bought a new KMC X10-L chain for £26. Fitting a new chain is simple especially with the connectors you get with the likes of KMC and Wippermann chains. I have the (£8) tool to remove the chain connector but it is possible to do it by squeezing the connector link together with just your hands.