For most cyclists, having a manageable range of gears at your disposal is a far greater benefit than owning the lightest bike. This explains why more bikes these days are being specified with either compact double 34/50-tooth chainsets or triple chainsets with their smaller graduations and lower gears.
The Sora 30/39/50 triple chainset has solid crankarms, as opposed to the lighter Hollowtech 2 of the 105 series and above, but the chainring teeth are ramped and shift the chain flawlessly.
The steel middle and inner chainrings make it heavy (the outer ring is aluminium), but we aren't complaining too loudly at this price.
The outboard bottom bracket bearings cost a further £17.99 and you'll need the special Shimano TL-FC32 tool or equivalent from Park Tool to fit them.
Don't forget that when upgrading from a double to a triple chainset you'll also need to buy a long-arm rear gear mech to account for the greater length of chain required for a triple chainset, and you'll probably need a new front derailleur too.
Some STI left-hand shifters will work with a double or a triple (of the 2008 models, 105, Tiagra and Sora are all able to run both double and triple chainsets) but some have specific shifters for double or triple.