Ex-members, called apostates, are an acknowledged phenomenon with known, predictable patterns, as documented by sociologists and religious scholars. To quote just one, Bryan Wilson, Ph.D. of Oxford University in the United Kingdom:
“The apostate is generally in need of self-justification. He seeks to reconstruct his own past, to excuse his former affiliations, and to blame those who were formerly his closest associates. Not uncommonly the apostate learnt to rehearse an “atrocity story” to explain how, by manipulation, trickery, coercion, or deceit, he was induced to join or remain within an organization that he now forswears and condemns. Apostates, sensationalized by the press, have sometimes sought to make a profit from accounts of their experiences in stories sold to newspapers….”
“Academics have come to recognize the ‘atrocity story’ as a distinctive genre of the apostate and have even come to regard it as a recognizable category of phenomena.”
This happens with other groups as well and even in marriages or broken friendships. The one who leaves sometimes goes a long way to explain how bad the relationship was or tries to justify that he abandoned his friends. This is a social mechanism and sometimes quite fantastic to listen to, but not a good measure to find the truth.
Some former members might complain about "bad experiences" they had or claim to have had. So, obviously they decided not to do something about it and left the organization. Maybe it was not the right thing for them. Just as most other religious organizations Scientology does not hold members who do not want to be members. Scientology practices do not work properly if done under pressure or false premises. So who wants to go, should leave or help to remedy perceived wrongs. Ex-members who try to make a living as "experts" on the faith they abandoned are clearly not neutral and not a good source for anything related.
An unbeatable way to find out something about Scientology is to go to a local church or mission and look around, get a tour and get informed. You can also go to a library and get a Scientology book. A pretty comprehensive book is one called "What is Scientology?" which tells about the Scientology belief and the organization structure (the book is also online since more than 10 years here).
There are also 18 basic books of L. Ron Hubbard in which he describes his findings and works in chronological order. Last but not least there are plenty of websites with free books or excerpts of Scientology material which the Church has put out over the last years.
If you are more interested what the Church of Scientology, the organization, does and supports, you should have a look at the Statistics page on this website.
Bryan Wilson: Apostates and New Religious Movements
Kliever: The Reliability of Apostate Testimony About New Religious Movements
What is Scientology? Book online
Scientology Handbook online