I am also a fan of the Fenix E01. However, I would not want to carry one on my keyring. The Pico is about 1/2 the size because they don't have to house a AAA battery. Plusses and Minusses. I will probably pick up a few more E01's over time. But I will also get some Picos...

...And this has absolutely nothing to do with my gear addiction. Just thought you should know...