Press release (for non profil organisation)

Hi everybody,

I propose to open this thread to determine the criteria for choosing and comparing press release services.

I'm looking for press release solutions for a non-profit education project and I found a lot of services, at different prices. I am not looking for a writing service, but only diffusion, with limited budget, but with high-quality articles that could really be interesting for journalists, not commercial promotion.

How do these services compare in your opinion? The number of journalists who will receive the press release? The average number of press articles published per press release?

It could be nice to have a real idea on how many article we can get on journals.

Thanks,

Do you have some reliable sources?