This will depend on what bird you have and what it's activity levels are.
For example Galahs are known to be prone to become overweight and suffer Fatty liver disease if fed incorrectly, whereas your Budgies tend to be much more active birds.
To begin with I only fed my parrots (Amazon, Patagonian and Hahns) a low sunflower seed mix (with their veg, fruit, nuts, etc etc). This is because they were not necessarily in the best condition when I got them with them being rescues and the Hahns was in fact very overweight. Even though they come out the cage they prefer to sit in one place rather than fly around or play with toys like the Budgies.
Now however they are becoming far more active when out and about so they are getting a higher amount of sunflower seeds in their mix.
You need to know your birds, their weight and their body condition and what activity level they have, and what sort of mix of vitamins and minerals they need and where they get this in their diet.
Sunflower seeds are not bad, in fact they can be very beneficial - providing they are fed in correctly.
