The price you pay for low cost oriental products like that is that you should expect for 'finish' them for the manufacturer. Use the wiring as an indication of where the connections need to go and then re-work them with proper mechanical connections, heatshrink etc.
Pay particular attention to quality and security of the case ground, strain relief and the quality of the switch and fuseholder. Also ensure (and add if necessary) that there is a fuse in the output line from the wiper - this is critical to avoiding destruction if you accidentally overload it at low voltage settings.
If you are prepared to do the above, they are still good value.