The Planet Waves Capo Tuner is an ingenious gadget that has rolled (most of) the functionality of a tuner and a capo into one unit. I say (most of) because this tuner doesn't have any way of indicating which note you are on, but only whether or not the note you are playing is on pitch or not.
Functionally speaking, I didn't find this was a problem. Unless you're de-tuning to some other tuning entirely, or re-stringing your guitar, then I find that most times my guitar is pretty close to standard tuning when I pick it up. It is for these types of tweaks that this capo tuner works just great - in fact, most of the time having a note displayed at me is a waste of time anyways, except for the situations I mentioned already.
So how does the tuner work if it doesn't have a readout? Simple - it uses a three light system, with a few different colors of lights. It is intuitive and easy to use. Because it works off the vibrations in your guitar, you can literally have it clamped onto any part of your guitar and it will work. This means you can use this as a tuner either on the fretboard, while capo'd, or just clamped onto the headstock as a tuner.
We've talked about the "tuner" part of this - but this capo tuner is exactly that - a capo AND a tuner.
As a capo, the Planet Waves unit works nicely. My main complaint against these spring loaded capos is that they normally don't have any sort of tension adjustment, which reduces their ability to perfectly adjust to different instruments. However, as you can see from the picture, this capo tuner does have a tension adjustment, which works quite well.
I've used this capo tuner on acoustic and electric 6 string guitars, and it worked fine on both. It is advertised to work well on 12 strings as well, but I haven't had a chance to test that yet.
I found the capo tuner comfortable and quick to use one-handed. Whenever you use a capo, there's going to be a bit of adjusting to get it to work well with the curvature of your guitar neck, but I quickly discovered that if I put it on a slight angle compared to the frets it works best for me.
If you'd like to get one of these for yourself, they're available for a good price at Amazon.
Full disclosure: Planet Waves / D'Addario was kind enough to send me one of these capo tuners for review purposes.
Planet Waves Capo Tuner Review:
Watch the Planet Waves Capo Tuner Review on Youtube