Yes it's worth it - DA really helps you focus on a clean trigger pull. Do it SHO and WHO - the only way you can pull that DA trigger without moving the sights is pulling the trigger in one continuous motion at a constant speed, be it fast or slow. Roll through it.
beretta 92d or any beretta 92/px4.
a sig 22X DAK
HK LEM
revolver
I'd get a TDA semi auto (I love the Beretta 92)- not only would you gain valuable experience with the DA pull, but also experience transitioning from the first DA trigger pull to the second SA pull - for TDA, remember the first pull is a roll, the second is a press.