Vantaggi
Compensation is decent, provided you're a competent negotiator (there are no fixed scales). If you were onboard at the time of the flotation ~2009), you'll have seen your options quadruple in value. They're effectively in the real-estate business - and with hosting for the major internet exchanges in Europe they're well placed to take advantage of people needing connectivity in Docklands and elsewhere - so business is good.
Svantaggi
If you're applying for technical role be aware their commitment to managed services ... doesn't exist. They are almost viciously Sales led - the UK MD and Sales Director double-team are canny negotiators but not receptive to change. Their CEO takes particular pride in regularly raising customer pricing even above their own power supplier cost increases. Cameraderie is limited - this is a place to work for money, not an environment to enjoy for itself.