Absolutely! Ethiopia is truly one of the safest places in Africa. People are friendly and like to help. Trickster you find everywhere in the world, also here, that's nothing new. Addis is a big city and you should take care of your belongings, especially around Merkato and Piazza.
Lalibela is also safe- no worries. Only if you come for ethiopian christmas (genna) or Timkat, when it's overcrowded it's quite often that thieves are around.
In general one fact might annoy you: the people/kids who will again and again ask you for money- please! dont give, this is for sure not their way into a better life.
Another thing which will happen: you will get charged 'ferenji' (white people) prices.-and normally there is no way around that