They both are mostly different but the feeling is similar. They both have that hacking vibe and a somewhat suspense

The story are totally different but the only thing i saw in common was gentle man/cold woman.
I will reccommend this if you like Cold woman/Genlt man drama.

Both of them is about a girl being bullied in a school and home thus they try to commit suicide.
Then they meet a older guy who and their life change.

If you like Student A then I really recommend Sachiiro no one room and vice versa.

Similarity:
1-Both of them have serial killings in the past.
2-Both dramas are about to find the serial killers.
3- Both the main characters are cold and show their affection to only their loved once.

Difference:
1- In Flower of evil, Do hyun soo has a family and in Nobody knows, Cha young jin considers ko eun ho her family.

(If I add point 2 it would be consider as a spoiler so I won't add it. However both of these dramas are amazing. they are MUST WATCH!!!)

Bedtime Hero and super star academy both of them are based on Super ability.
Bedtime hero is more about the life of people with super ability while super star academy consist about ability from constilations.

They are not completely similar but they both have the concept of special ability.
Super star academy consist about the power from twelve constilations.

They both have high school students solving cases
In devil inspector two boys solve cases with help of a cop
If you like SGHSI then you will really like devil inspector