The problem with any SMT, monolithic driver like the TB6560 is the extreme cost of repair. Things go wrong in the real world... motor leads come loose, or wires get connected wrong, or power supplies spike, etc... and when something does go wrong, doing what amounts to surface mount repair to replace an expensive chip that encompasses every function of the driver is just not reasonable. Although some people do it.
And on top of that, the TB6560 itself is fragile. It does not incorporate protections offered in many other driver chips (e.g. the SLA 7076 or A3977 are much more rugged) so frying it is very possible.
All in all, I personally recommend drivers that use separate power drive transistors. They can be easily replaced at very (very) low cost and so make your investment in the driver as a whole more secure. If something goes wrong (hint: It will!) then you can replace the drive transistors easily for a few dollars with an easy, through hole repair that anyone can pull off with the cheapest soldering iron.
And.... honestly? Competing with the insane claims and prices of these scam artists from China is going to be very, very, very difficult. People just don't seem to have a sense of "too good to be true" anymore.
And finally... a good design for the 6560 has already been done:
There are other places in the market that might be better to look into: Why isn't there a low cost kit or open source design for a general purpose, parallel port opto-isolator? Some people worry about isolation, others don't (I think using an old PC and Turbo CNC without isolation is the smart move... I don't want my nice iron anywhere near a mill) so putting isolation on every driver is an unnecessary expense. It should be available as an option to add to /any/ controller by plugging it in between the PC parallel port and the driver. But I can't find anything on the market that does it...
Other ideas: Design a CNC mill that can be built from large, heavy, very low cost materials which are commonly available from junk yards or hardware stores which uses a small, light, easy to ship part to join those base structural pieces and provides precise alignment. Design an open source, high power, discrete bi-polar driver. Design an effective encoder/control system that accepts step and direction signals and allows the use of DC motors with a drive system (gear box or belt drive or ...) to replace stepper motors. And so on... lots of good ideas out there.