1. it comes with batteries - they are almost empty will last for a day or two, so add cost of new set of batteries which will double the cost of already overpriced tail light.
2. changing the batteries is a problem - you need patience and additional tools to do this simple operation.
3. flashing strobe mode is too slow in my opinion
resume- if i would have a chance to check real product before buying - i will never ever buy this item - very very poor design , ergonomics is none, overall - ten bucks thrown away.
p.s. finally i have bought a better tailight in 99cent store for a buck, plus another buck for 8 batteries. ;) LOL