I have a client with an iMac and when I moved the Airport Extreme to the basement during the remodel, the iMac continued to connect to the router, rather than the Airport Express that's less than 20' away. Since none of the other wireless devices were connected to the Express, I added a 1 to the SSID, connected the iMac and 'Forgot' the Extreme's SSID. It's working much better. They can still connect their hand-held devices (they generally move while they use their phones, but not the other wireless equipment, so roaming still works well enough. When both Airports had the same SSID, the speed measured on the iMac might be 25+Mbps, or it might be 2Mbps.

FWIW, I have a Luxul XWR-1750 and I use my iPhone 6 & a Windows-based laptop, as well as two Roku. My iPhone NEVER has a problem connecting to it or holding onto the network, but it always had problems with the Arris from ATT Uverse.

I set up the Luxul at the house where the iMac was having problems and it didn't make much difference when I used the same SSID, but I installed it where the Airport Extreme is located, not close to the iMac. I didn't connect it up there because I had consistently seen good performance with my phone and laptop, but they didn't hunt for a network the way the iMac does.

I would chalk this up to being a Mac thing, rather than a Luxul thing.