It's quite simple: -
No soldering, nor CE labels, no messing around. No DVM required for testing. Plus you got refills by the dozen so next time you have a too-bright LED it costs nothing but time remembering where you slid the pack of these little beauties.
It costs about 4 quid from here and here's the originator's web site.
Don't try it with high power lasers though (I mean... who would?).