Thought you said it was, "a friend"?
The plates will do the job just fine - the issue is the difficulty of rendering over. There were multiple other options that may have been preferable.
Sistering the joists and Bow Tie-ing into the sistered joists would have been a much better option for a start.
Using traditional pattress plates and lining them up at equal centres would have been better and maybe then rendering over wouldn't have been necessary.
Or the render could have been terminated above with a bell bead and started again below.
Or the rendering could have been carried out first and then the traditional pattress plates installed.
As it is I think I'd go for external insulation and then render over that