Does it have the contrast, brightness, conectivity and glossy surface like a tb display?
All the screens I have seen so far do not come close to the tb display.
Weirdly I just purchased a HannsG 23" 1080p touchscreen (TN panel) for only 150€ and that's about as close as I ha e come so far to a TB display.
I found this review of it, with some interesting data:
http://www.digitalversus.com/lcd-monitor/acer-k272hul-p20417/test.html
And here's some data about the Thunderbolt display:
http://www.anandtech.com/show/4832/the-apple-thunderbolt-display-review/6
The contrast looks to be almost exactly the same.
Maximum brightness is not quite as high (300 nits vs. 375) although the Acer still gets so bright that it's painful to use in a normal indoor setting. I have mine set to 30%.
I know these are two different reviews with two different measuring techniques, but it looks like the Acer might actually have slightly better backlight evenness (7% vs. 8%).
The Acer doesn't have all the same features as the TB display, since the TB display is really more of a docking station than a monitor. So the Acer does not have a USB hub or TB connection or camera. It does have speakers but they are horrible. But, it's still a very good display, which is what its supposed to be.
Unfortunately it's matte instead of glossy. Some people prefer matte but I prefer glossy. But for $330 I'm willing to live with matte.
If you haven't had an IPS display before, I would definitely recommend it. The difference is pretty huge. I used to have a 24" 1080p TN panel and no matter where I sat, either the top or the bottom was washed out. Now I can look at my monitor from whatever angle I want and it looks great.
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The pixel density isn't a huge difference, 109ppi vs 118ppi.
FYI the two Macbook Air models are 135ppi and 128ppi respectively.
The other factor for me is desk space. I don't have a huge desk. Ideally with unlimited budget and space I would go for the 27".
It's definitely IPS, all the new Dell models are PWM free IPS panels, from LG. However it seems the 25" panel is from their sub-brand. I forget the name but it's part of the LG brand. Hard to say if the quality is different.
I know the MBA has higher pixel density but for some reason the pixels on my 27" display seem very small in comparison. Maybe it's because the display is so much bigger that I instinctively try to view it from further away, maybe to see more information.