It's completely safe. Attitude and Herbiesheadshop are very reliable.
Here are some tips.
DO NOT use another person's address, get then sent to you. It's better not to get them sent to the address you plan on growing at but I'd do that over sending them somewhere else unless that other place is a place where you get regular mail.
DO NOT order more then 100 dollars of seeds per order. If using a credit, debit, or gift card you will most likely be flagged by the card company as many times they automatically flag larger purchases overseas, especially if you have never made one on that card before.
If you plan on using a pre-paid gift card you will have to call the number on the card and request to be able to use it overseas, that takes about a week to go through.
Always use the stealth options if available.
Note that the majority of your wait time will not be because of the seed company or Royal Air which is the carrier most seeds get to the US on, it will be the wait at the US Customs/USPS sorting facility in Long Island, NY. I have tracked a few orders where they sat for up to 9 days at that facility just because it's so backed up there. This is an advantage and is the main reason buying seeds is safe.
Research the strains you want. Depending on your skills and what you are looking for this is a very important decision.
Good Luck!