The only Smith whose first name begins with "P" that I could find, living in Oban about that time, is a Peter Smith, born about 1864. He was a hotelkeeper, married with three kids as of 1901. He was not a native of Oban, however, but was born in Airdrie in Lanarkshire.
A decent candidate for the guy on the invoice, but there's no way to know for sure if he's definitely the one.
By the way, I found out a bit more about what happened to Julius Assur Friedlander (son of Montague). He didn't die in 1951. Tracing him was a bit trickier because during WW1 he changed his name to Freeland; like many British people with Germanic names during the Great War he doubtless thought it both patriotic and discreet to adopt a more Anglo-Saxon sounding name. He eventually died in 1963 in Northampton.
