Low level for me is anything that goes over each and every single part of the disk one by one. Whereas standard format utilities and whatnot just write a few items to the disk and call it done.
As for updating the bad sector list? I don't care. First failure and it is out. These are old drives that I am digging out of boxes. The first thing I did was a read test using SeaTools. Simple, and pretty fast. After the read test I booted up and used smartmontools to check the SMART status. If there were any read errors before, the drive is put in the discarded stack.
I now have a few drives left that show no errors in the SMART status (usually a good sign).
After it has passed those tests I would like to run one last final test, the read/write test as you call it. It used to be called a low level format in the likes of PC Magazine, but whatever.
If no such tool exists, then I will have to quickly write one which works by just opening the raw device on FreeBSD and writing 10 MB of data, and then reading that same 10 MB of data and comparing the two. Would be slow, but it would work, and it would show me errors if they did occur since FreeBSD would hang on the write.