It's very hard to say much definitive about the effectiveness/results. Did you try w/o the flash or other methods to compare results? In a situation like this my preferred method is backwards bounce and I have to think it would have worked at least as well. What were the other settings?
What I can say with some certainty is that the speedlight added very little to the image and I doubt it would have looked much different if it hadn't been used at all.
I was using 100 ISO film at the time and the available light in the shop would have dropped the shutter speed too low to have given anything like enough depth of field for a hand-held shot. Hence the use of flash. I didn't take a comparison shot without flash for that reason, and because I only had 36 shots of Ektar 100 to play with that day.
Backwards bounce - towards two multiple-paned glass shop windows? Given that I was using film so I couldn't fire off a couple of test shots and chimp, I don't think I'd have wanted to risk the light literally going out of the window, or spurious reflections showing up in the glass fronted and topped surfaces of the display counter. Also, I think the chap playing the part of the shopkeeper might have got a bit hacked off with me firing several shots to try various bounce angles, not to mention the other visitors to the museum who wanted to look round the shop without some big mook with a camera monopolising the place. Hence the one shot take.
What were the settings? No EXIF file with my film camera, so it's from memory. Somewhere around 1/80th at f/5.6 (I should have used AE and gone for f/8 to give slightly more depth of field). Flash and camera on ETTL (no ETTL II on this camera) with no compensation used on either.
The speedlite added just enough to the image to provide some detail in the darker areas of the shelving and the darker areas of the chap's clothing to stop them looking an underexposed mess, and retained a lot more detail in the window at the back, which would have been totally blown out without the flash. In all, this gave pretty much just the amount of fill flash I was looking for; subtle and so it wasn't obvious flash had been used.
As has been said, the dome diffuser is just another tool in the box and there's no magic bullet; no single thing will work in every situation. However, quite often when doing documentary style photography it's not possible to use multiple flash units, large or cumbersome diffusers, or to chimp away to check the results and modify bounce angles, positions, etc. until the desired effect is obtained. That's what I like so far about my cheap dome diffuser, it's fairly portable and can give some nice looking results.