I would not recommend water cooling at this stage, nor spending £60 on a cooler. If you want an aftermarket cooler get the Coolermaster Hyper 212 Plus
The one he has linked is a sealed unit though Calaye, he does not need to do anything other than fit it. Yes ofcourse there is always a chance it might crack and leak so its important to make the right decision
What about the downside of it costing £60? I highly doubt he'll be that seriously into overclocking to see the benefits, better to start cheap then upgrade as/if necessary. Unless money is no object of course.
Intel 2500k does have the Turbo speed boost, i have mine set at 4.5ghz so even if he isn't into overclocking a decent cooler would be advised.