We have been testing as we go, instead of testing all at the end. It's more expensive up front, but it might save in other costs/time down the line. Also we preferred the idea of freezing each blast once (and thawing for transfer), instead of 'freezing, thawing for testing, re-freezing, re-thawing for transfer' if you test at the end of embryo batching. Some clinics might not give you the choice.
The day before EC I thought it was worth asking if it was ok to proceed with transferring one of our 2 frozen embryos that were already tested as chromosomally normal, and the consultant said it was ok.
So like in a regular fresh transfer scenario, I've been taking progesterone from EC day, and the idea is we go ahead with transfer on day 5, providing one of our 2 frosties thaws ok. And the embryos from this cycle will be frozen and tested if any make it to day 5.
Actually looking back at our previous fertilisation numbers, we have had 3, 6, 6, 5, & 4 fertilised from our five ECs over the past year. So pretty in line with usual for us.