I carry a double set of Epi-Pen Jr's for my youngest son. No matter where I am at. I also carry a full bottle of Benadryl as well. I have used an Epi-Pen before, and yes, it does amazing work. The method that is recommended by my son's allergist dr and regular doctor is Benadryl in mild issues (flushed face, itching). Give it and watch carefully. Epi-Pens are for when the &^%$ goes down. Having seen my son go into anaphylaxis twice, once you see it, you know what to watch for. Anytime there are hives, puffing up, where the person cannot breathe right, they must be injected - and then given a dose of Benadryl immediately after. Two Epi-Pens can be given, if the first wears off - but directions MUST be followed. With Epi-Pens, the patient MUST be taken to emergency care immediately. This affected me a lot last year with taking him hiking - because I didn't feel safe enough to take him with me. I have overcome much of that fear, with him now being over 2 years old.
There are 2 versions of Epi-Pens: adult and jr, which have different doses. They should not be stored in cars. They must be kept at a normal temperature, not refrigerated nor hot. They are not cheap I can tell you. I get 2 sets of 2 each year (one for a home e-med kit and one for on the go). While my insurance covers all of it for one kit, the second kit I have to sign that "we need it" and pay a co-pay. Cash price is..... $453 PER KIT.
Having said that, an Epi-Pen saved his life after finding out he was allergic to cashews. I'd pay cash if I had to. They are a miracle with a needle if you need one.