There are no backdoors in Bitlocker, nor does Microsoft have access to your keys. Bitlocker is FIPS 140-2 compliant which is acceptable for healthcare, banking and most government entities. Bitlocker works pretty well and I haven't personally had any issues using it. It doesn't require a TPM to encrypt your drive but the TPM adds extra security. The thing to remember is if you do a BIOS update you need to pause the encryption.