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The display itself works great over a USB connection with my 15" rMBP--very little lag, quite usable. Can't comment directly on Pencil capabilities since I, like most of the people on this planet, haven't been able to get one yet, but I know pressure sensitivity isn't supported yet. Supposedly the developers are tackling this next, since they've just recently gotten their hands on an iPad Pro for testing!
 
I've talked to someone on another forum that uses both DuetDisplay and Astropad. He seems to like DuetDisplay as a second monitor, but uses Astropad when it comes to drawing in Photoshop/Illustrator/Flash.

I only have Astropad (and no pencil yet). But I've been pretty happy with the low latency -- but I'm only an amateur/hobbyist sketcher/painter so I'm probably not hammering at it like the pros would.
 
I've talked to someone on another forum that uses both DuetDisplay and Astropad. He seems to like DuetDisplay as a second monitor, but uses Astropad when it comes to drawing in Photoshop/Illustrator/Flash.

I only have Astropad (and no pencil yet). But I've been pretty happy with the low latency -- but I'm only an amateur/hobbyist sketcher/painter so I'm probably not hammering at it like the pros would.
This my experience as well. Duet for simple extra real estate, Astropad to use like a cintiq.
 
I worked with Duet most of the day yesterday and it worked great. Apparently the first version of Duet had an issue with high cpu usage. However that is not the case with the current version.
 
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