LightBurn for the C3D board is $40, not $80.
The C3D sometimes takes a bit of tuning, depending on the machine. It’s a drop-in board replacement, but there’s a learning curve involved.
If you post some specific results with “here’s what I got, and here’s what I wanted” we can likely help. As Blake says, general complaints without asking for or providing anything specific isn’t giving us much to work with.
Slow speed is likely Smoothieware - it has a limit to how fast it can process GCode. We (C3D and LightBurn) are testing changes I made to the Smoothieware code to improve this. You can also use GRBL-LPC which runs significantly faster. If you try to push Smoothieware faster than about 80mm/sec it can skip, which might be why you’re getting bad results with the images.