If a photographer is just getting into the indoor flash thing, I continue to recommend that the first light modifier you buy is the Gary Fong Light Sphere. In spite of all my experimentation with dozens of different modifiers and techniques, you can't beat the Light Sphere for simplicity and consistency. I remember the first time I used it to make a group photo with Senator Jackie Speier when she visited an upholstery class that was held on one of our campuses. I literally took it out of the box, attached it to a NIkon D600 speedlight mounted on a Nikon D50 body, and by simply following the instructions, took a very acceptable class photo. The Light Sphere was a relatively new product at the time, and was something my subjects had never seen before. It was introduced in late 2004, and since then one of the many versions has always been within arm's reach.
Hail Mary: The photo at the top of this post was taken by simply mounting the Sphere onto an on-camera flash, holding the camera high overhead, and framing the shot using the tilting LCD on the back of my T-2. I mentioned that I find the T-2's simple "tipping" panel more practical that the T-4's that is fully articulating. Notice that by using a reasonably powerful flash at a relatively short distance, there is enough light to balance the street visible through the window behind my subjects.
I will say that there is no perfect variation. The originals were designed to fit certain families of flash heads and while easily attached to the flash, they were easily knocked free with the slightest bump. Later models incorporated a Velcro cinch strap which was more secure, but impossible to install with only one hand. When the collapsible variant became available, I settled on that one, as it was easily stuffed into a camera bag and used as a "lens cozy" for my medium zoom lens. The "dome" portion was detached and stored separately. Good thing, because I've taken to using the dome as a diffuser when taking white balance readings.
Packing Heavy: I normally carry two of everything when I'm on an assignment. Either as redundancy for backup or a chance to get multi-light creative, you will find two flashes in my bag. In being prepared, I normally use a round-headed Godox flash for its more even light pattern. But when the Light Sphere is needed, I switch to a more convention square-headed speedlight. Gary Fong claims to have made a new version that can be attached to a round-headed flash, but I haven't seen one for sale, and since I always have a suitable flash, haven't felt the need.