They are legal under federal law but some states banned them (MA, CA, IL and some others). In most of the states which banned them, licensed manufactuers can have them. VT is an exception where no one but police can have them.
In states where you can have them, you need to file a form with fingerprints and photographs and pay a one-time $200 tax. You must also get a police-chief to sign the paperwork or if you own a corporation, you can sign yourself and skip the fingerprints and photos. After a backgrund check, you can pick it up.
Shooting with hearing protection on is like wearing a raincoat on a sunny day. Imagine how nice it is to shoot with friends and talk -- and I don't mean through the amplifiers on the new headphones.