I have one of these vises, and the screws and dovetails are useless. I just leave it loose unless something needs to be restrained. Then, I tighten the stupid gib wingnut and do fine positioning by sliding the base around. One of the screws was so bad, I permanently removed it. That axis is just pushed around. Another problem is that you cannot drill straight using parallels. The center bar is proud of the ways, so if you put parallels down, they teeter-toter. Also, there is a huge casting void next to the fixed jaw, so the parallel sits at the wrong height. If I need to drill something straight, I use an angle plate or 123 blocks.
This tool is useful for holding small pieces and is safer than holding parts in your hand. It doesn't even clamp that tightly.