I have an eggspert, and it works great. Has a bit of a kiddie feel to it, but you can't beat the price for a lockout buzzer, and it takes up to six players!
The random picker works just fine as well, and you can set it for anywhere from 2-6 for the picker to pick from in case you have less than six players.
I forget how many batteries it takes, and don't know how long the batteries last; however it does have an ac jack, but doesn't come with a plug, but you can buy a universal at radiocrap or elsewhere, perhaps Amazon as well.
The complaints in the reviews I read before I bought mine had something about short contestant cords, but I didn't think they were too short.
Yes, it does make a sound when you buzz in, and there's even an option of a timer to go with it so if you want to set up for a contestant to have 5 or 10 seconds to respond after buzzing in, that's there too, but the noise is annoying.
in short, it's a bit cheesy, but it works.