Primedice's symbol is a crown with a dice, and it's true that in the realm of dice sites they seem to be king. The website is an important part of the bitcoin world and probably one of the oldest and most trusted gambling site. This is the first important part of Primedice, the site is old, extremely active and largely trusted. It never had any solid accusation of scam or dubious activity. Seems like your coins should be safe around there.
Primedice is old but not old-fashioned! Indeed what you can find online is in fact not Primedice but Primedice2, the old site got a brand new design not so long ago and I have to admit it's a pleasant part of the site. There is a very easy user interface but with also a rather cool design with animations and live stats.
In addition, Primedice also has an interesting faucet system with an amount that will increase along your wagered amount and your chat activity. Because yes Primedice has also a rather famous chat with a rainbot and even different rooms for different language (as it's not unusual to have 2000 players live better pick your language).
So, easy, well designed, secure, trusted... What else could you expect from a dice site?