I have used these plugs for several years now, soldering my own cables for my effects board and making instrument cables. The quality of these plugs is absolutely outstanding for this cheap price. I can hear or see no difference between these plugs and more expensive ones.
The only tricky part is soldering the mass contact to the plug, but with a little bit of excercise (probably after two or three cables), you will do just fine and have good, long lasting plugs for your instruments and effects for barely one euro.
You have to be careful though when using these plugs directly into your amplifier, because of the angled jack it sometims blocks other inputs (for example on my Laney IRT Studio)