The MainStreet CommerceBusinessFlow SDK is full of features... that's the good news. Using those features is next to impossible. They offer absolutely nothing for documentation, tutorials, or other online/print reference material. Their answer to this is "drop us an email and we will answer your question". Not very helpful when you are trying to develop.
As a previous reviewer also mentioned, their support is horrible. The mailbox you send your questions to seems to be something they only get to when they have some free time. So expect to wait several days or a week before you get an answer.
We've also run into performance issues with the system. Again, no help from support.
I cannot recommend this package based on what we've seen.