That's a pretty broad statement that needs a qualifier... they work well "in the proper application".
Most UHF "mobile" duplexers, are just simple notch types that will offer you some isolation from your own transmitter, but not from anything or anyone else. Even then, you only get about 65dB of isolation... so you better be using low power. They work "well" for portable repeaters and duplex subscriber units... real repeaters use real duplexers. Lee
