Ginkgo biloba is a great herb for many different health problems, particularly peripheral circulatory problems (or problems related to circulation to the arms, legs and head). The "flushed" feeling you mention would indicate to me that the ginkgo is promoting increased circulation to your head, which is great for your brain, as well as for eye health. The flushing may just be temporary, especially if you just recently began using ginkgo, or you could try reducing your intake a little.

Of course quality is important when it comes to herbal supplements. Many "cheap" products don't go through the rigorous quality control and inspection that some companies (like Nature's Sunshine) put their products through. In fact, I've personally been to the manufacturing facility for Nature's Sunshine and was amazed at what a high-tech, high-quality operation they have. Apparently, it's not uncommon for them to reject raw herb materials from growers because of the poor quality of the herbs.

Anyway, I hope this helps. I've written a detailed information page about Ginkgo Biloba with some of the scientific research (from peer-review medical journals, etc.) available on its proven uses and benefits:

Ginkgo Biloba

Feel free to check it out and let me know if you have any questions.