Most cockatiels don't like fruits so you're lucky if yours will eat them. I'd suggest giving them veggies every day and possibly adding some other healthy foods to the diet.
I'm not familiar with Brown's but they do advertise that they're nutritionally complete:
http://www.fmbrown.com/products/pet-birds/good.html I'm assuming that the nutritional completeness comes from the brown pellets in the mix, because seeds alone simply can't offer complete nutrition. Do your birds eat the pellets?
There are a lot of nice brands of nutritionally complete pellets but it's not always easy to convince birds to eat them. It's usually easier to get them to eat Nutriberries, which have the same ingredients as pellets but not ground up as fine, so they look like seed balls. They're easily available at pet shops and your birds would probably love them.
If you're interested, here's our article on the best diet for cockatiels:
http://www.littlefeatheredbuddies.com/i ... ldiet.html