I've tried the free gh/s but i don't know if it's a great idea to continue "mining" there
To withdraw the funds from your free-miner you have to invest
that reminds me to a 'piramidal' word

Um, yes.. the free miner is for testing purchases. We would go bankrupt if we allowed people to withdraw without purchasing, we tried that at first and ended up with 2000 signups with 100 views on our bitcointalk thread.
-Sahra
I know, but you can try to make different offers and not just a free miner from which you can withdraw just if you pay for another service.
Maybe change free points to obtain miners if people make X referrals, or if people share your site to X social networks
it's easy
