They're okay - mine is the bass version of the Fly 3 & I bought the extension 'cab' to take it up to a whopping 6 Watts!
The amp takes batteries (6 x AA IIRC) as well as PSU that comes with the unit, so it's portable & good for taking outside.
It has the usual controls (Gain, Volume and EQ) plus variable Compressor, Overdrive and Sub, which are okay to a degree.
It has headphone output & line-in, so its good for jamming along to music from your 'phone.
Overall, it's quite useful, but the tones aren't great & I found that it rattles a bit with lower frequencies. I think I paid about £75 for the amp & extension cab, which I think is fair enough.