It can be set pretty closely to the muzzle, within a few inches or a couple feet from my experience. It should pick up 2 guns that are close to the unit if that is what you wanted. Or you can set the sensitivity of the device to not pick up other shooters that are close by.
It can be set to fire the radar when a shot is fired or it can be turned on for a predetermined amount of time, if a shot is not detected in that time the radar will go dormant again. If a shot is detected the timer will reset, it will continue to reset the timer and keep the radar "on" as long as you keep shooting inside the time limit.
The unit wants to know the weight of the projectile that is being shot, I am not entirely sure how picky it is about this. I saw it pick up and give accurate numbers on a 338 while it was programmed for a 700 grain (.50) projectile.
I was very impressed with the unit, it was great to just pick it up and set it down beside a gun on the line, take 2 seconds to roughly aim it at the target and start getting MV numbers. With this thing there is virtually no reason not to track your MV at almost every range session.
It had a decently sized memory capacity even without the SD card installed, you could go back to a string of fire and check all the data as you pleased. We had 27 different strings of fire on it, some with 15+ rounds per string, was easy to go back and check data if I wanted to.
I will say that it took me a little of playing with the unit to figure out the controls, but even without reading the instructions and a short brief from the owner of the unit I was able to fiddle my way through the options and have the unit up and running in under 20 mins the first time. After that it was maybe 2-3 mins from the time I took it out of the case until it was ready to collect data.
Long story short. I want one.