Hi
I just bought a UR824 and am pretty happy with it right now.
I bought the UR824 for recording, but I also had live mixing of our very small band setup in mind. The low-latency mixing with effects feature of the UR824 thus was a big plus for me.
Until now I have used the device for live mixing one time and it worked rather well, but I have a few suggestions that might make it even more usable or user-friendly:
The ChannelStrip window could easily be twice as big. I used it on a small laptop computer and had trouble with the very small display. Especially the EQ-Curve display could be bigger.
Also the EQ section is a little misdesigned in my opinion. I might be wrong, but who uses shelving filters for LF??? Some might use it for HF but even there I (and most audio people I know) much prefer a peak-filter. There are only 3 EQs which is OK, but if you want to tune the sound a little bit, just one fully parametric EQ is not enough. Why don’t you just implement 3-full parametric EQs instead. That would be a real benefit.
I am a signal processing engineer and have built both the user interface and the dsp side of EQing before and I think a fully parametric EQ would not be more expensive than a shelving-EQ on the DSP side (you probably use biquads for both the peak-EQ and the shelving EQ), so this is just a user-interface thing and could easily be done in an update. I’m really looking forward to this! 
Come on… Shelving filters…
The EQ thing is my biggest point. The second one is of lower priority to me and of higher cost to you:
I personally use a lot more EQing than Compressing. I don’t know about others - anyone? So I would prefer to have 12 channels with EQs to 8 channels with EQ and Compressor. Maybe in the future there could be an alternative to the ChannelStrip effect that is just an EQ and needs less processing power so that more channels can be FXed…
How’s everybody else’s opinion?