It seems to me that the difference is that with UBI you can use the time that you would otherwise be working to prepare for a new job, look for a new job, or to do work that doesn't pay (e.g. art).

On the other hand, a low wage job takes up the same amount of time as a regular job but doesn't provide many of the benefits (e.g. financial security, sufficient discretionary money to pursue your goals, the ability to purchase a house, etc.).