Luc DeGrande and I have done a lot of work with this chip. So far, we are very impressed! It has run at 5 amps (it's rated at 4) for a limited time and not fried. I've personally disconnected motor wires mid run, powered it up without logic power (which may kill a TB6560 as per the data sheet but won't kill the 6064), and generally abused it in many ways without any issues. It is a chopper, so it does buzz and hiss a bit if it isn't adjusted just right. And there is a little mid range resonance in the lower microstepping modes. But it's generally a very nice driver.
We now have a nice PCB layout and kit available at:
www.linistepper.com
It joins the "Linistepper" family adding bi-polar drive for larger motors. As with the other drivers there it is compatible with the PMinMO standard connector for step and direction with the 4Axis / Pulse / power board for easy connection to a PC and to limit switches, relay driver, logic power, etc...
Luc's site:
users.skynet.be/ldt/CNC%20electronics
CNCZone discussion:
www.cnczone.com/forums/open_source_contr...64ah_pcb_design.html 
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