A tuner and a metronome in one. I bought it mostly for the metronome functionality since it's way cheaper than analog ones.
The screen dim is nice - the display is still visible somewhat, but the backlight is off, so it's less distracting and saves batteries. The built-in leg stand is very convenient, too.
The tuner itself feels somewhat more sluggish to CTC-50 and struggles more with E1 on bass. Plus for 430-450 chromatic range, though, since CTC can only do 440-449.
Make sure to put good batteries - when they're dead, it still functions somewhat, but the screen will not light up and the sound will be continuous. I thought my unit came broken cause of that, but it was actually okay. I just had to change the batteries.