quoting myself… 
Too big for a keychain light - compare it to a Tank007 E09
which is: 19 grams including a 10440 cell, and 70mm.
Maybe 300 FCL, not 300 lumens 
*FCL= Fake Chinese Lumens a new designation for Lumens created specifically for Budget Light Forum for converting Chinese claimed Lumens to actual Lumens.
1 Lumen = 1.7403 FCL approximately, and may vary from one light to another.