In case you were wondering why I was leaning towards this photo as being pre-embarkation, I don't know... it might be the fact that none of the people visible appear to have any rank or insignia on their tunics (AFAIK collar badges were not issued until a month of training had been completed)... or the fact that the photo is too posed like graduates from recruit training (the rifles all slanting inwards)... or that the uniforms are too uniform (except those two soliders whose collar are unbuttoned) like they just came from stores - the pockets not yet stretched out from cramming things into them... Or maybe it is just my (albeit rusty) sergeant-sense tingling, but the soldiers in your photo just have an aura of 'shiny' and new - not like veterans of anything.
As to my comment on the lack of insignia - coloured patches started being issued in Mar 1915, and before that (from about September 1914) metal numbers would have been worn on the shoulder straps - I see neither on the uniforms pictured suggesting that the photo was taken before Roberts embarked in Feb 1915.
Also in reading the narrative for E.A. Roberts, I noticed a few details that I believe are slightly varied from the records: for example "Edward sailed from Devonport England, on 'Oriana" on 15 JAN 1915 to Alexandria, Egypt." - that event occurred in 1916 when he was returning from King George Hospital in England.
He appears to have embarked for the Gallipoli campaign on the Defflinger (aka SS Huntsgreen) and while the date is difficult to read on the Casualty Form, the letter on his service file dated 28 Sep 1949, gives his embrakation date as 11 Feb 1915. Similarly I read his initial transfer to the Stretch Bearer Section as dated 8 April 1915 (vice 3 April)