Yes, the #110 snow guards can be used on cedar shake roofs, many synthetic roofing materials as well as most slate and tile roofs.

The #110 snow guard can be attached to lower sloped roofs but you should make sure that the roof membrane isn't penetrated in a way that will expose the roof deck to the elements

The #100 snow guard has a slotted bar that is used for retrofit applications where the roof materials can not be easily lifted.  The slots allow the snow guard to be hooked on to the fastener that is securing the roofing material.

Snow guard placement will vary depending on the application but the first course is usually installed 12" up from the insulated wall at the eave.  And subsequent rows are usually placed approximately 18"-24" above the first course.

Quantities of snow guards will vary greatly depending on the type of roofing materials, the rafter length, the slope of the roof and the snow load in your area.  Typically snow guards are recommended to be installed with 3 rows.  Rafter lengths longer than 24 ft. should have consideration for additional rows being installed half way up the roof.

The shortest answer is that snow guards, also known as snow cleats and snow stops, can be used to hold ice and snow on the roof to prevent it from sliding off in an unsafe manner. The snow load is held on the roof pitch while small bits of ice and snow will melt over time. Make sure to follow all included installation instructions to ensure your snow guards work as expected. This will ensure you get the best protection from bad weather in the winter months and avoid accidents.