Here's my take on triple vs dual monitors: I've head double screens for a very long time now, but wanted to upgrade to 3, first thing you should not here though is that preferably all the screens are the same. I'd even stick with same brand, if you try and do 3 screen with say a 23 a 24 and 23 model the screens will never really align when playing games, also gamma and other color settings are extremely difficult to get to match. As the view is so wide and immersing some games are going to need addons like widescreen fixer to move some controls into the center off the screen as otherwise you need to constantly pan your head left and right. Being such a wide screen though, they become more peripheral vision than actual focus-able screens if you get my drift. Also some games will also simply straight out not work on triple monitors so keep that in mind, maybe do some research into which games you play before deciding on three screens.
As for productivity, three screens has it's advantages, when I was coding I was able to view the code on one, be connected via ftp for upload to the server and view the coding results on the last one, but again your field of vision is only so large that you have to pan your head constantly. Now you might wonder where's the problem with that? Well I got a sore neck after a time since I didn't adjust my sitting position as needed and just turned my head.
To alleviate that I actually went BACK to only having two screens, so I wouldn't do this bad habit any longer. The immersion, from 3 screens, while great wears off after a while, and for most productivity tasks two is enough, as again your field of view is only that big. With just two monitors they take up a combined width of 44" with a third that would be 66" or for those on metric 1.67 meters. That's a big table you need for all that screen!
However I do HIGHLY recommend a monitor stand of some kind, I have a custom built one with one of those uplift standing desks. For most normal sitting positions, most regular screens simply do not have enough options to adjust height and position. Again hate to once again moan about ergonomics but when you spend a lot of hours in front of a screen it really does start to matter. Just glancing over the product page the stand is very low, but at least it has a vesa mount. If you were in the USA I'd say get a monitor arm from monoprice like this one
http://www.monoprice.com/Product?p_id=5402&gclid=Cj0KEQjwyK-vBRCp4cymxermx-EBEiQATOQgh7q7dJQQc-I6ykJrs1b_Y64QENjl5hYKWUuKeLXTUnIaAqw58P8HAQ&kpid=105402 but I haven't lived in the UK in some time now so no idea what good online retailers are nowadays.