Unmodified flash? Without umbrella, softbox, or bounce? Can I use that and still get good results?

In a word: yes. You do not always need flash to be modified.

For instance, you may intend the look. One single, unmodified flash can give you a hard look, and that may be exactly what you are after, like in this high contrast B/W self portrait:

So sometimes you can use it to deliberately accentuate the hard look of a photo. So this is the intentional hard look.

At other times, you are mixing in ambient light to take away some or all of the hardness. That, in other words, is the minimized hard look. One way to do this is to use another flash; another way is to mix in ambient light, like here:

That was made with one flash; see it on the right here:

The key in all examples here is that the flash may be direct, i.e. unmodified; but it is not where the camera is. In other words, it is off-camera flash (OCF).

Whenever you want to try a new look or technique, my advice: yes, try it and see. You may be surprised by the results.