The original Stern board has riveted optos, and it tends to fail.. you have to drill them out, desolder, and replace them.
This replacement board uses standard hardware to install the optos, instead of rivets. MUCH easier to replace.
Next, there is a red and green LED for each channel.. The red is lit when the opto is operating, and the green LED indicates when the opto is blocked/open. Makes troubleshooting a breeze!
And I warrant the board for 6 months. How can you go wrong?