From my understanding about sunflower seeds is thus. They are not bad if they only get a few in their diet. Sunflower seeds are high in fat, as all seeds are, but they are usually so many in a mix that they go for them first as they are easy to open and get the meat out. Safflower seeds are just as high in fat but it takes so many to equal that of sunflower seeds. Plus side of safflower seeds is they have to put a lot of effort into getting to the meat.
IMHO, 20 seeds is ok. I think you can get broken sunflower seed at the grocery store. You may want to try some fresh food as a reward.
All of my feathered overlords get some seed and nuts daily. Their weights are stable. Over all they only get about 10% of their daily feed in seed and nuts.