Hello Cruzer090
I have been using the UniFi AP Flex HD for about two weeks in our 4.5 room flat. I have very good reception everywhere. Even on the balcony I still get 90% of the full speed. The flat is at least 40 years old and has many concrete walls.

I can't tell you how it compares to the AC-PRO. However, Unifi's APs are very powerful :)

The design of the Unifi AP Flex HD is also more suitable for the flat in my opinion.

Hello Cruzer090

I replaced my AC-Pro with the UniFi AP FlexHD a month ago and can say that the FlexHD is at least equal to the AC-Pro in both range and throughput. Subjectively, it even reaches further and is a notch faster (without measurements). In addition, its form factor is more practical than the AC-Pro plate, which is more difficult to place without screwing it to the wall.
-> I can highly recommend the UniFi AP FlexHD.

Tip: In order to know where the front of the UniFi AP FlexHD is (you can't see it without looking at the back where the cable comes out), I drew a small black dot on the front so that it is always positioned correctly.

Greetings ATM