ByteFence is safe while it is a free program, but this doesn’t mean that you need to buy the full version of the program.
If you’re not using your computer for anything too important or if you have backups for everything, then you might as well use this free virus scanner. There are risks involved with asking for money from people who largely cannot afford to pay money in order to clean their computers. For example, even if they want to make sure what they’re buying will be worth it (which ByteFence promises), if most people don’t have other options before purchasing bytescape products then there’s really no competition or assurance that these prices are reasonable and fair.