Built-in long lasting battery
Built-in tripod mount
Calculates joules for bb weight/size/velocity
Shows distance bb can travel
Easy to use
Can show either english or metric systems
The rpm and rps aren't accurate: mine only shows 3 different values.
The screen is too dim to see without the backlight on.
The screen with the backlight is visible indoors but hard to see outside.
Mine came with the battery fully charged.
If all you need it to do is velocity or joules, it works very well.
If you want to know your rps/rpm, it doesn't work very well.
If all you want to know is if your gun meets local field fps requirements or just curious about your guns' fps, it works very well and is much cheaper than anything else.
Airsoft GI sells this same chrono branded as AIM for $10 more.
I am rating this 4/5 because the screen is hard to see outside (and everywhere without the backlight) and the rps/rpm feature doesn't work well but the fps is very accurate and that is really all I need it for.
Rating: [4 of 5 Stars!]