It all depends on whether you can bounce the flash off the ceiling. Small diffusers like the Stofen project some light forwards (and back which can be a waste) but the flash head points upwards so most light goes to the ceiling. That's fine if the ceiling isn't too high and is white.
The alternative is a diffuser that makes the flash itself into less of a point source, and therefore softens the shadows you get with direct flash from a single point. These tend to be much bigger because they have to be in order to spread the light.
IMO a good solution if you can't bounce the flash is to get some of this flexible thin polystyrene foam sheet used for packaging, and wrap that around the flash, with the head vertical, so the sheet sticks up above the head and acts like a big reflector. It's rather like a 'whale-tail' diffuser that you can pay lots of money for, but the DIY version is cheap and disposable. You can also roll it or fold it to fit the camera bag. Secure it to the head with a (high-tech) elastic band.
This is one made from card, but the thin foam sheet is a lot easier!