Relieved to report I got my soft power DTV through from HCMC yesterday finally. Application submitted 24th April, pending approval 25th April, approved 10th May.
3 points of note from my experience:
Hanoi seems to be much quicker at processing the applications within Vietnam at the moment if you are considering an application in the country.
HCMC approved my application on a Saturday evening - this is the first report I have seen of "out of hours" approvals from this embassy.
I had an active METV in place at the point of approval of my DTV. A caveat to this is that I got a new passport in between the METV and DTV being granted.
This group has been invaluable to me so hopefully this information helps someone else.