Flights from priceline.com.....are they reliable?

I was looking on priceline for about $620 tickets to go to Romanian with my other two sisters and my cousin and I found them and stuff but I'm only 15 and my mom doesn't think or know anything about price line like if it's safe and will get us to Romania without any problems occurring. I also read something on price line on how the flighting time may start from 5am and 2am the next day..... ?... If you've gotten ticket from this site please let me know how your flight was . Thanks guyssss!