I wouldn't pull it on oki, honestly, it only has 3 active frames, making it really hard to meaty with (not to mention if you mess up, you're stuck in a huge amount of recovery).
As far as blockstrings go, even though it's a really slow move, as long as you remain unpredictable with it, put it out anywhere you'd like, provided you're close enough to the opponent. It's really good for resetting pressure. But if people see it coming, expect yourself to get hit out of it.