My OET Experience:
After many unsuccessful attempts in IELTS, I have finally got grade B in OET in my first attempt. I would recommend taking OET for anyone stuck at 6-6.5 IELTS writing.
I did the three tests in OET official book. For writing I practiced writing one letter each day for two weeks and roughly timed myself as it was very difficult with three little ones.
I went through benchmark checked letters and I also bought assessment of three letters by benchmark.
In addition, I joined telegram group called oet rivals which was quite helpful in terms of writing materials. They have oet grammar book which is superb.
Best of luck
( request for prayers)