I would very strongly advise against this - there are far too many things that can go wrong.
USB is not a reliable storage format, devices fail occasionally. What happens if the office burns down? You could lose the PC, and the backup if you're not careful. Ideally you need to be taking the USB stick home with you so its in a different location. This means more plugging and unplugging, which will increase the risk of failure.
How often do you plan to run the back up? Once per day? If you have a failure, you're losing an entire days data. And what if you forget to plug the stick in? You could be losing days worth of work.
Also, you are not protected against a ransomware attack. If you get hit, it will encrypt your USB files too as soon as the disk is inserted.
There are far too many things that could go wrong.
The backup solution I use costs just £10 a month, for unlimited offsite storage. It backs up in real time - as soon as i save a file, it uploads it. In the event of failure, im losing minutes of work, rather than days.
It also contains multiple backup sets - if i get hit by a ransomware attack, i can roll back files to a previous version, or even roll back to what the files were a day, week or even months ago.
There are plenty of affordable offsite backup solutions out there, i'd strongly recommend looking for one rather than using USBs.. the benefits are significant