In a nutshell - it really boils down to how you use them. What seems to work best for me after various arrangements of screens is this:
The large screen in the middle is 28'' Asus 4K (PB287) [approx 160 ppi, about 8 megapixels] the screens at the sides in portrait are 23'' DELL IPS U2312HM [approx 110 ppi and about 2 megapixels] and obviously the little ones above are your truly - the ipad replacement parts [approx 265 ppi and about 9,5 megapixels altogehter]
I should note that my workstation has quite a number of displayports at it's disposal although this particular setup could get away with something as low as four of them (three if you use multi stream transport hubs) and two legacy connectors. I have three graphics cards, a 7950 FleX edition driving the 4K over DP and DELLS with legacy connectors and a Club3D 7870 Eyefinity 6 card driving the ipad screens. In addition I have a XFX 6770 Eyefinity 5 card sitting idle most of the time - just because it would be quite a hassle to take it out (Water cooling would mean to have to redo the loop).
So what I was doing with them previously and what do I think of it.
Shortly - I used it as my primary screen for about a half a year trying various different arrangements of auxiliary screens around it. The results are .. well .. mixed. When they are suitable for a task at hand the experience is rather awesome, all these pixels in your face, all the information you can access with just a slight eye movement. Quite an improvement for productivity - however - in my experience the advantages of additional screens start getting diminishing returns after about third screen or so.
Main downfall of that setup was ergonomics. If you sit with these screens in your face for 6+ hours (my distance was between 30 and 40 cm from the eyes) you will start noticing the eye strain. Few times it was so bad that after 10+ h particularly intensive days my left eye was seeing black spots. The new arrangement with these as auxiliary screens works much better. As an added note - DO NOT put your primary screen or anything you need to make more use than occasional glance higher than your eye level when you sit with straight back - I tried it a long while ago for a little bit with different screens and the experience is not a good one.
After about 6 months I was starting to get a bit worried about the eyestrain and I had developed a more or less consistent mild headic so I asked for additional hardware budget from my employer and got a 4K screen for the primary screen. (That is a longer story why I'm using these at work instead of home but in a nutshell wife was not particularly understanding if I wanted to erect something with exposed powered on PCB's to have 3 additional screens as I already have 5 of these 23'' DELLs on my desk at home and have a small kid and cats)
So what would be the conclusion. It is awesome for stuff that scales well (I am using it mostly atm to throw up there papers or figures to glance at when I write my papers or analyse results) and painful when it does not scale well (say, trying to make use of some menu that does not support any scaling at all in some program). I must also add that when I started this project the 4K screens were costing arm and leg plus kidney - with the introduction of affordable 4K screens I would probably not start this kind of project today unless I would have a specific need for ~10'' high resolution screen for something. For a PC it would cost about the same to get the cheapest 4k instead.
Oh - one more thing which I have already mentioned. If you plan to use something like that as your primary screen you need a damn good stand to put it in your face.
What next ... well ... would it not be interesting to build a projector out of these ... I have not built a projector before so it would be certainly be interesting project. I will think about it - perhaps one day.