One thing I will say about the Lightsphere is that I don't have to
think about bouncing so much like I did with the omnibounce. With
the omnibounce I have to angle the flash head, decide if I want to
bounce off the ceiling or wall etc. With the Lightsphere i just decide top
on or off and only need to touch the flash when switching between
portrait or landscape.
Omnibounce and Lightsphere work very similar. Omnibounce is a wide-angle reflector increasing the angle of illumination of the flash light to something like 180 degrees. Lightsphere is a "bare-bulb" modifier that we know very well from many manufactorers (for example Broncolor's "Balloon"
http://www.bron.ch/bc_pd_ps_en/detail.php?nr=955 and many others). A "bare-bulb" reflector is an even "wider" reflector and it increases the angle of illumination to something like 360 degrees.
If there are no bounce surfaces around, the only difference betwen bare flash, a wide reflector and a bare-bulb reflector is the angle of illumination. Light and shadow characteristics remain unchanged because neither reflector changes the size of the light source any relevant way.
Things look difference if there are sources available from which the flash light can bounce. Then, due to the bouncing (and not the reflector), shadow characteristics are changed because both light coming directly rfrom the flash and light arriving indirectly ("bounced") will illuminate the object. The higher the amount of bounced light relative to direct flash light, the "softer" the resulting lighting will be. A "bare-bulb" reflector in a typical residential house will create slightly more diffuse light because the amount of bounced light will be higher. On the other hand, a "bare-bulb" will require more flash power to achieve this effect. And this is a bit of a problem with on-camera flashes because they are not very powerful and one will suffer from even longer recycling times.
In short:
A) the shooting environment plays an important part in how your light modifier will affect the final picutre.
B) "soft", "diffuse" ertc. light is only a secondary effect of on-camera light modifiers.
C) Due to B, in a shooting environment where bouncing is possible, the differences between bare flash, Omnibounce and Lightsphere will be minor.
Omnibounce was once very among press photographers and journalists because a lot of on-camera flashes did not have built-in wide-angle reflectors that were really wide enough. This situation has changed.
Another point is that image quality of digital camera at higher ISO settings (ISO 800 and up) has become really good. High ISO capabilities of a camera are important in flash photography because it allows the photographer to mix in more ambient light without incurring a significant loss of image quality. The less flash light in a picuture, the less important the characteristics of the flash light source, the less the need to use gadgets like Omnibounce etc. With a modern digital camera, on-camera flashes can be used as a "fill-in light" even in rather dark lighting conditions. This is great news since this is what on-camera flashes are good at.