Robins are not known for constructing super safe nests - they do like to be out in the open and will not nest in an enclosed box. At least on a covered platform they are better protected from the elements than many nests I have seen them make. Wherever you put them, make sure that they are not accessible to predators - under eaves is fairly safe unless there are vines, etc. nearby that can be climbed.

It seems to me that robins can take care of themselves. They're ubiquitous and common (and wonderful). They arrive in early spring, eat mostly anything, build their classic nests out of grass, and then leave (they're flocking to leave right now). I'm suspicious of products that people market to attract wildlife. Most of them are more beneficial to people--especially the sellers--than to wildlife.