No you do not have to have the blinder professionally installed. Actually its not that hard to install. The owners manual shows you exactly how to hook up your blinder M-25. As for Installers I like MEGAMAXX in marietta off cobb parkway next to the big chicken. They did the install on my 2005 Honda accord sedan. As for two heads vs four heads on a sedan, in my opinion the M-25 works great on midsized and full size cars. The M-45 works the same, the only difference is 2 extra heads which can give better protection if you drive something like a 300C chrysler sedan. That car has alot more surface to cover versus a honda accord. As for laser from behind, its very,very rare if at all. 98% of officers fire at the front. You could always try 3 heads in the front and 1 head in the rear if your concerned at all. Hope I helped.