Q:Is it legal to download music from the sites reviewed at this site?
A:Yes, it is legal to download music from sites that provide it legally. Most of the sites reviewed here are Russia-based and are subject to their laws. The legislature there enforces compulsory licenses, which means that anyone can get the license to distribute and sell music as long as they pay for it somewhere. In the US if you plan to sell a certain CD, you have to negotiate with the labels, and that's why the original Napster got shut down by the courts - they violated the law by not obtaining the licenses from the RIAA mob.
In Russia if you prove that (a) you keep track of what you're distributing (log number of downloads) and (b) you pay to the collection agency, you're legal to distribute any music you want. The collection agency (ROMS and FAIR, quoted in the Wall Street Journal article) will then re-distribute the money to the copyright holders.
Q:Is it save to give credit card details to pay for mp3 music online?
A: Yes, services reviewed here use 3rd party processing systems. That means that services do not receive information about your credit cards, your payment is processed by secure services authorized by Visa and other systems, transactions are secured by certificates.
If you still feel uncomfortable using your credit card to make payments, you can find service that accepts e-currencies or other payment methods like pay-by-phone. Or you can use PayPal to pay on any music site