Birkenstock Betula

I am hardpressed to understand and try to search online to see what is the difference between the two. The price difference is about $ 40 - $ 80 cheaper for Betula then for Boston, any idea is greatly appreciated!

I do not know. I have two pairs of Betula. I have no reason to believe they are not authentic. They lasted for years, and I bought them cheap on eBay. They are sandals. Perhaps Betula are sandals. Dunno.