I bought one of these for around 100$ USD a couple weeks ago.  Rather than posting pics and specs, I'll just give the Amazon link.

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Just for a change, I'll start with the "bottom line" question first.. Is this actually good enough to be worth the price for a violinist/fiddler what wants to record audio and video of their playing?

Yeah, I'd say it is not a bad option for that.  Since it can also function as a USB mic and webcam, it is a decent value for the price.  Not hard to use, very small, and the video looks decent and I'd rank the sound as "seriously ok".

Meaning, it's not "professional" grade sound, but it is quite good, and better than I was expecting from a small device made for non-technical users.  I'd say it can do well enough to be as good as any single camera angle production you'd see on youtube, for example.  And actually it would sound better than most of what you hear there.

Good enough for most purposes, if someone is looking for an "all in one" device with a fairly short learning curve that doesn't take setting up much gear to make a recording with.  It has surprisingly nice stereo sound that seems fairly "natural" with acoustic instruments at close range (10 ft or so, I haven't tried further than that yet).

Now into some more technical observations.  It uses "mid/side" style mic-ing to do stereo.  Some engineers like using mid-side and some prefer binaural.  I'll just say that both have advantages and disadvantages, but either can produce very nice results.  You don't have to make physical adjustments to the device to change the stereo image, it is menu selected from mono to 150 degrees spread in 30 degree increments.  A pro would find that too limiting, I would bet, but it's enough flexibility and versatility for an amateur in most cases.

No real EQ on the device, just a low cut (rumble) filter that can be turned on or off.  Some wouldn't like that, but since I'd usually rather record "raw' and do any eq or other treatments afterwards on the computer, I'm fine with it. 

Battery life is kind of limited.  Since the unit is doing a lot of work, it is going to eat batteries.  But the batteries it uses are common (AA), and you can buy a power supply to use with it as an optional extra.  You can also...

Disclaimer inserted here..- This "trick" is not one provided in the manual and while I am doing it, if *you* do it and wreck your gear, neither I nor Fiddlerman.com will accept any responsibility.

... turn on the unit with battery power and then plug in any sort of USB power supply and it will happily use that and leave the battery alone for as long as it is plugged in. 

It does not come with a case.  Considering the LCD view screen and the lens, I'd find some small case that could be padded for carrying it, if I was going to take it out of the house much.  But I'd say it is no worse than any consumer-level digital camera in that regard. 

It is not really well designed to use hand-held.  It was obviously mostly intended to be put on a tripod and left in one place when actually recording, I think.  There are ways around that, but I'm just saying that as it comes out of the box, the lack of a hand grip and the handling noise that you get with a little box with microphones mounted on it make putting it on a tripod or setting it on a table or other convenient bit of furniture the obvious choice.

The display is obviously pretty small, but enough to tell if someone is in the frame or not. If you want a big display that you can see while recording, the device can output to an HDMI TV or monitor.  You can also plug headphones into the Q2, if you like hearing monitor when you are recording.

So I'd rate the device as not really "pro" (anything short of several thousand bucks' worth of gear that you'd need to take classes to learn to really run well isn't going to be), but definitely not a "toy" either, and capable of managing well enough for a bit of home recording and probably quite adequate for someone wanting a single device that could do recordings of practice or for critique for the forums, group project participation, Streetjelly, youtube, podcasting or etc.

For an "all in one" type device that could literally fit in a pocket and can run off very available (and reasonably cheap) batteries, I think it is not a bad option in the price range.