There are credit score estimators available for free, many call these scores Faco Scores. Unless you purchase your Fico score from Equifax, Transunion or My FICO you aren't receiving your true credit score. Experian the third of the three major credit agencies no longer sells or provides Fico scores.
What I have done in the pass is purchased my score from Equifax and Transunion when I have gone in to pull my free annual credit reports from AnnualCreditReport.com. I have also purchased my credit report and credit score from My Fico.com. I did use my debit/credit card to pay.
As for being safe any of the agencies web sites would be safe as they already every detail of your credit history.
I did hear on CNN the Clark Howard Show that the government is going/trying to pass a Bill that will allow one free credit score from the three mojor credit agencies a year, similar to the free annual credit reports.