I guess I'm going to find out, a set of EAP225 APs will arrive today.

To answer my own question: I did some testing with the EAP225 today and the conclusion is that there is no significant difference in signal strength or range compared with the M5 in this home use scenario, so I am keeping the M5 for now.  I am also going to try a Ubiquity AC LR.

@Jeehaa Hey did you keep the M5 in the end ? How was the roaming using the EAP225 ? Did you have the omada controller set up as well ? 

@Jeehaa You are better off deploying more access points vs. trying to get more range from existing ones.
Remember that even when a AP has more Tx power, your devices (phones/tablets/laptops/IoT) don't. Maximum Tx power is also regulated, and basically every AP can run at the maximum.

The ceiling mounted access points (EAP, Ubitquiti, Cisco, etc.) which beam down, cause they're designed to be ceiling mounted. I think the M5s are unidirectional, but cannot find any data on that.