I'm going to leave my original response here, but I am also going to add an update to this thread, as we are now waiting to make this math recommendation.
inHIsTiming,
We actually know what our recommendation will be in this area now, so I can gladly share it with you!

In the new ancients guide, we will include a schedule for Singapore 4A/4B for those who need to back up in Singapore when coming from another program. For students beyond Singapore 4A/4B, we will give a choice of doing Singapore 5A/5B or Teaching Textbooka 6. If kiddos are at the Singapore 6A/6B level (having completed 5A/5B or its equivalent in a different math program), we will most likely be recommending only Teaching Textbooks 7. We may not be carrying Singapore 6A/6B, due to its use of the rods system as opposed to the 'x' and 'y' system used in algebra in the U.S.
If moms aren't sure which level of either Singapore or Teaching Textbooks to use, kiddos can take a placement test at both sites to help them with placement. If kiddos struggle with math or are average in math, we will recommend using Teaching Textbooks on grade level. If kiddos are advanced in math, we will recommend using one grade level ahead of Teaching Textbooks. Some moms have jumped their kiddos up even further than that with Teaching Textbooks, but we don't find it beneficial to rush ahead that far, and won't be recommending that route.

We do feel that the elementary years spent interacting with the parent while doing Singapore Math does a great job of setting a strong foundation in abstract thinking, mental math, and difficult problem-solving.
We have read about and researched Teaching Textbooks, as well as using it within our own family, and are quite comfortable recommending it for the middle school years. We have found the coverage to be thorough and the real-life explanations to be well-done. Our oldest son has completed TT6 and is half-way through 7, enjoying it thoroughly so far. We are looking forward to most likely offering this math program for the middle school math years.
Blessings,
Carrie