I don't have digital mixer, but I did look at Behringer Flow 8 when I was buying.
Upsides... If there's something specific you wish to achieve, then yes, digital mixer has some mixing advantages. But in my opinion, if only one keyboard and a microphone is used (plus maybe a guitar), then digital mixer doesn't show benefits. Actually, for live performance, even if two keyboards are used simultaneously, analog mixer is easier to use (and cheaper).
The main advantage of digital mixer, as I see it, is in studio recording. In case of Behringer you mentioned, you can record up to 8 separate tracks on PC: i.e. two keyboards (in stereo), plus two microphones, plus guitar and you still have 1 channel free. In live performance, by assuming there are enough inputs, we're mostly interested on two channel output -and that, every analog mixer can do.
Some may say "well, doesn't hurt if one have more options than currently needed" -that's true. It's just, that it's easier and faster to setup analog mixer to our liking, than that's the case with digital mixer. But there's a catch: most analog mixer don't have audio interface. Means, one needs separate audio interface for recording music on PC. In such case, I would recommend something like Yamaha AG06, which is a mixer with built-in audio interface. Actually, if only one keyboard is planned to be used (+microphone), then even cheaper Yamaha AG03 (which I have) is enough.
To summarize my thoughts... yes, digital mixer is better because of flexibility and features it might have. But only you can answer if it has upsides for you.
Bogdan