Snow guards for metal roofs

I was searching the internet and found a good deal of information on what they call snow guards. I ended up purchasing 38 of these lifetime guaranted polycarbonate guards that screw or glue to the metal roofing. Since my steel is the "Imperial rib" type which means I have a major rib every foot and two minor ribs inbetween - the folks that sold me the snow guards (Polarblox) recommended that I screw them down using three screws each. These blocks have six holes on one leg - they recommended two in the far top holes and one in the bottom center for each one. They also recommended silicone under and around each guard and to use a washered screw(those I have from the construction of the building). They said to stagger the rows every other major rib from one purlin to the next down the roof starting with the first purlin from the eave. Sounds pretty simple - I wanted to get some advice before I get started. I've seen snow guards doing their job on several buildings around the area and they seem to work pretty well. I did read that one drawback was the increased snowload on the roof due to snow not getting off as quickly. I built my building with engineered trusses 2' on center with a purlin every 2' ft so I'm probably OK for snow load - at least here in PA. Much obliged for the advice.