I have had various keyring torches, and the weakness is generally they use some button battery that doesn't last or hard to get. This uses a standard AAA battery, and basically you can't have a smaller or lighter AAA battery torch, I have mine on my car keys, and gets bashed around with no issues so far.
Excellent light for the size, much brighter than say my iPhone 7. Has three levels and lowest is good if you just want to read something. The brightest is plenty for looking for something or going over uneven ground in dark.
I liked mine so much that I have bought another six for presents.