Casio G'zOne Commando

Full-duplex is, of course, better. However, speaking from experience trying a lot of speakerphones, I can tell you that a good half-duplex speakerphone an be almost as good as full-duplex, depending on the noise environment (and/or noise suppression technology.)

A bad half-duplex speakerphone is an awful thing, but there are good ones that might surprise you. Sometimes we have trouble determining which kind it is; you really can't tell in normal conversation; only special tests will tell you for certain.