this seems like an interesting project but i am a bit confused about what exactly it downloads. you call it "block headers chain" and claim it is "about 150 MB on mainnet" which is where my confusion is. every bitcoin "block header" is 80 bytes and by the time of writing there are 570849 blocks so the size of the file should be 45,667,920 bytes or 45 MB (which is the same as the blockchain_headers file that Electrum downloads).
so what is the extra ~100 MB for?