@kennetrose I have no idea why it isn't done more. It takes up a cycle, so some people probably don't want the delay. 2 out of 3 women will be receptive with 120 hours of progesterone and in the UK they seem to take a trial and error approach to IVF. The ERA seems to be marketed towards women who have had unsuccessful transfers.
There is evidence for the microflora, I read a book on preparing the endometrium for IVF success and I was convinced to do it after reading the chapter on the subject, it cites this study, https://doi.org/10.1016/j.ajog.2016.09.075 which separated women with more than 90% lactobacillus vs those with less than 90% lactobacillus, the outcomes were statistically significant:
Implantation 60.7% vs 23.1%
Pregnancy 70.6% vs 33.3%
Ongoing pregnancy 58.8% vs 13.3%
Live birth 58.8% vs 6.7%
So hopefully this explains why at 0.00% I have never had a BFP.
Unfortunately getting a sample from the uterus is fairly invasive, it isn't as easy as taking a swab. In some studies they have swabbed the transfer catheter tip, but the best way to assess the microflora is to get a biopsy. It isn't painful, they just use suction to remove the stuff that's removed with menstruation.
The EMMA and ALICE can be done alone, my friend is having a stand-alone EMMA after the trio test showed issues with her microflora which she's had treatment for. They put her on the mock FET again.
If I were you I'd be inclined to do a mock FET, you will take estradiol, they will monitor your lining, you'll then be on progesterone for 120 hours, they'll bring you in and take the sample and send it off to the lab. The ERA is relevant for a 2 year period. So this way if you move on to IVF at some point in the next 2 years you'll know about your transfer window. While also knowing about the microflora.