Dozens of defectors have deserted Islamic State, shattering the group's self-proclaimed image of a "jihadist utopia", according to a new report.
Since January last year at least 58 individuals have left the group and spoken publicly - and the number is growing, researchers based in London found.
Some fled after they were disappointed by the "quality of life" in territory controlled by IS and realised that the image of luxury goods and cars that lured them to join in the first place had failed to materialise.
Defectors were also found to have left after being outraged with the group's brutality and disillusioned by corruption in the ranks.
The study, published by the International Centre for the Study of Radicalisation and Political Violence (ICSR) based at King's College London, said reports of defections have been "sufficiently frequent to shatter IS's image as a united, cohesive and ideologically committed organisation".
It added: "They demonstrate that IS is not the jihadist utopia that the group's videos promise; and that many of its own fighters have deep concerns about the group's strategy and tactics."
Researchers tracked 58 individuals - 51 male and seven female - who have turned their back on IS and later spoken out. This was described as a "sizeable number but likely only a fraction of those disillusioned, ready to defect, and or willing to go public".
The report suggests the pace of public defections has increased, with almost 60% of the cases reported in the first eight months of this year, and nearly a third in the three months to August.
In a sign of IS's global recruitment strategy, defectors represented 17 different countries, including two from Britain.
Most felt the group - also known as Isil - had not lived up to their expectations, while four narratives emerging from their stories were singled out in the report.
:: In fighting - Defectors criticised IS's involvement in fighting against other Sunni rebels, while there were also accusations that IS had failed to confront the Assad regime in Syria.
:: Brutality against Muslims - Many complained about atrocities and the killing of innocent civilians, although brutality was not a "universal concern" but "caused outrage mostly when its victims were fellow Sunnis".
:: Corruption - Most incidents involved individual commanders mistreating their fighters and favouring some over others but corruption was not seen as "systemic".
:: Quality of life - A "small but significant" number of the defectors expressed disappointment about living conditions. They "quickly realised that none of the luxury goods and cars that they had been promised would materialise", while Westerners found it hard to cope with shortages of electricity and basic goods. There were also suggestions that the experience of combat failed to meet fighters' expectations of "action and heroism", with one describing his duties as "dull".
Defecting from IS is "complex and dangerous", with those who succeed in fleeing the group's territory fearing reprisals or prosecution once they return to their home country, the study said.
It called on governments to do more to remove obstacles that prevent defectors from speaking up, saying their testimony could be help prevent potential new recruits from being radicalised.
The report stressed it "does not attempt to excuse, justify or glorify people's decision to join IS", adding that some are "likely to have committed crimes".
However, it said: "They joined the most violent and totalitarian organisation of our age, yet they have also become its victims, and their stories can be used as potentially powerful tools in the fight against it."
There have been suggestions that police plan to enlist former extremists in a bid to stop more young Britons being lured to fight in Syria. At least 700 have made the journey.