I found this video which compares the sounds of various Basses from Bass Guitars, to Bass Ukuleles, and even a Bridge EUB (Electric Upright Bass) so you could hear the differences in sound. The UBass with the Rubber strings does produce a sound that's "Double Bass like" but it does make a great Travel Bass, just as the Ukulele makes a great Travel instrument too. The Double Bass being Acoustically imperfect (like the Viola and even the Acoustic Bass Guitar) is what gives it a really special sound while still being portable.
