So far, I've uncovered two issues with this radio during my testing:
1. When the squelch is turned all the way up to mute the incoming signal, there is still a low level white noise that is quite audible. It's not that noticeable in a mobile environment, however it's very obvious with an external speaker in a base station setup. It's actually a little annoying. This is a fairly minor issue, but I've never encountered a radio that exhibited this exact squelch behavior.
2. The second issue is a more serious one. In my mobile, I use a powered external Texas Ranger speaker. I use this speaker because the radio is very difficult to hear with the top off. When I use a powered speaker with the 680, I encounter what most people would call talk back....except the radio isn't supposed to have talk back. I don't hear the same thing when I plug in an unpowered external speaker. In my jeep, the "talk back" is quite loud and there is no way to get rid of it.
This has actually been a problem with certain Uniden CBs in the past; I had the same issue with a Uniden 520. With the 520, the feedback from the external speaker was so loud that I was unable to use a powered mic because it resulted in serious squeal. On that radio, I actually added a relay in the radio that would disengage the external speaker upon mic key to solve the problem. Doing something like that on this new radio might not be such a bad idea.
Hopefully the folks from Uniden will see this and can address both of these issues in a future update to the radio.