A study by Consumer Futures found that only half of branches affected by the change offered significantly longer opening hours, while people still had to wait in queues to be served.
The restructuring programme is leading to large and small post offices (PO Mains and PO Locals) moving into retail stores, with new operators and locations.
The consumer group said customer satisfaction rates with services were high, but 60% of the 2400 people surveyed said they could see no tangible benefits.
Of the branches studied, just half offered significantly longer hours and customers in some were queueing for five minutes or more.
Andy Burrows, of Consu-mer Futures, said: "Although customers are generally satisfied with current provision more needs to be done if POL is to deliver necessary service improvements and to ensure maximum value for money from such a large funding package."
Consumer Futures said extending opening hours should be a priority, as well as moves to shorten queues.
Margaret Lynch, chief executive of Citizens Advice Scotland, said: "Making sure people don't have to queue for too long should be a priority to encourage customers to use the full range of serv-ices the Post Office offers.'
A Post Office spokesman said: "The Consumer Futures research is based on just 53 branches during the first year of our transformation programme.
"We now have over 1100 main models offering new modern branches for communities across the UK, offering customers an extra 27,000 opening hours a week.
"In total almost 2000 new main and local post office branches have been transformed, providing over 50,000 extra opening hours a week.
"These branches are proving extremely popular with customers recording 95% customer satisfaction levels."