Fact is that pellets contain everything the a bird's organism needs. One other advantage is that you have less waste compared to conventional seed mixtures.

I don't want to tell you whether you should feed your birds on pellets or not. You have to decide this on your own. But please note that most budgies need some time for getting used to this unusual food stuff. So it is recommended to serve conventional seed mixtures and pellets together in the beginning. Then reduce the content of seed mixture from day to day within two or three weeks. At the end of this period, your budgies will hopefully eat the pellets. My budgies never ate one single pellet. They just played with this colourful food even when they were hungry.