They are absolutly illegal to have. The SD GFP specifically marks it in their hand book that you are not allowed to be in possession on this type of optic (handheld and firearm mounted alike) while hunting. It is not illegal for me to own in my state but it is illegal to have with me while hunting
After kill locators are legal in many states, but if yours is not, then use the other techniques. "Optic" would be the questionable word, as these are not optics, but I would place a call to GFP for clarification.