We also have twice used the Optum/ Binax tests. The first time was in our hotel in London. We used our IPhone and the hotel's Wi-Fi. We just propped our phone up on the desk against the wall.
The second time, we used them at home 3 days before boarding. They worked great. However, we will NEVER do that again; flying to a foreign country 3 days before boarding, not knowing if we will be positive or negative. It is very stressful, even though we did have travel insurance.