I hope this rather long post will be of some use to others.
My goal in RE interiors has always been to make the most use of ambient light and, often, to include several areas in a photograph so the viewer gets a good idea of how the spaces interact with each other. Most of the images I have posted here are automated blends of a 7 shot, 1 stop bracket (usually 4 or 5 of the 7 available frames) processed in either LR/Enfuse or Lightroom HDR. I don't care for the typical HDR look (or the color shifts) so I have taken great pains to process carefully and to find alternative methods.
I've bought and worked with some luminosity masking plugins for PS and found them mostly disappointing, worked on hand-blending (especially for window pulls), bought Photomattix (not using it - too weird and makes me leave LR/PS too often), and tried some other Exposure Fusion plug-ins. They all have their faults.
I've studied and worked with multiple lights on site but it's very hard - at least for me - to get ambient looking light with flash set-ups. And single light set-ups just looked fake. I've read the books and understand what to do but, at least in my area, open plan houses are common and the larger public rooms are difficult to light with small flashes.
So I have moved to Flash-Ambient as the first choice almost all my work. First, you need something larger than a small speedlight(s). I use a RoveLight and it is perfect. I can bounce into very large rooms successfully and , since it is battery operated, there are no cords to move or get in the way. It's cheap (for what it is) and very useful. My first exposure for each set-up is a flash bounced from a wall behind the camera. That is followed by my 7 shot, 1 stop bracket bracket which serves to provide me with a good ambient exposure to blend with the flash and a back-up if an EF blend is necessary.
Back in my office I pick the ambien shot that looks like it will blend best with the flash shot and open that and the flash shot as layers in PS. I put the ambient one on top, put a black mask on it which causes the flash exposure to be the base of the image. I set the mask to "luminosity" rather than "normal" which eliminates color shifts. Then I paint white on the mask as needed to hide the look of flash, fill shadows, add highlights, change the apparent direction of the light, and make it look as much like ambient as possible.
I am taking slightly longer on site and slightly less time in post. I enjoy post so that's not a problem. My clients are very pleased with the results. I'm posting a couple from last week's work. The entrance door has always been a problem. There usually is nothing close to bounce from and there is inevitably sensor bloom around the windows. The Flash- Ambient approach cures most of the problems. The bathroom shot shows how effectively the Flash-Ambient technique handles multiple rooms and angles in one shot.