Female seeds i have grown out from DP have been all female so far. However ive found it can be very easy to Hermie them through stress. One WW plant grew 5-6 male flowers just a week into flowering which i picked off, and it flowered beautifully after that with no more male flowers. At a different time another was over ferted and hermied in week 6, this is more dangerous to your crop as it can be hard to spot. Removed this from room straight away. No more probs.
Some sites will tell you how resistant to hermi/how uniform/how stable etc each breed is. Generally if you dont stress them you will very rarely see a hermie.
In my opinion female seeds are very useful to growers who want to maximize their growing/flowering space, usually on their first couple of grows, without having to throw away males, or waste space. After that, if you have room, i would then move on to regular seeds.