I was lucky & DD has one for a few months then gave it up by herself. DN was still on his aged 2.5. There are definite pros and cons but if it helps him settle and get some sleep the short term gain is probably worth it!
Wholly worth it in my opinion. Was a really good sleep association thing for my DD and she has been a great sleeper from 6 months onwards. Yes, of course they form a dummy habit if they have one, but it's a habit that can be broken. Babies and small children find sucking v soothing...nice way for them to fall asleep.
Totally worth it!! I didn't give on to DD until she was 7 months & I was exhausted. She fell asleep on her own & slept through! She's 3.9 now & spoke very early & clearly. At her 2 year check the HV said, "you can tell from her speech that she's not had a dummy"!! We've always called it her pipe. She only ever has it to sleep & once she hit 2.5 it was strictly for bed & it still lives under her pillow just in case!! DD2 is 2 weeks & she already has one!!
Both mine LOVED their dummy. It was never in all the time. Mainly at night and when tired. We'd always carry the 'emergency' dummy. My two were always in control of when they had it in (within reason of course, what I mean is I never shoved it in!).
We got rid of the dummy to the 'dummy fairies' when they were about 3ish. No problems. No teeth issues. Absolutely no speech issues. Just happy children.
We often see the new dummies on the shelves at Sainsburys and they both go 'ahhhhh' with nostalgia.