Just dropping in without knowing the context: I've used Bitcoin Core in the past to double spend a transaction with 0 fee that was still stuck after 2 weeks. Double spending isn't necessarily a bad thing, but there's a reason you shouldn't except a transaction without confirmations either: it's not guaranteed to confirm!
For normal Bitcoin use, you shouldn't need to double spend anything. If the fee is too low, use RBF or CPFP.

Needless to say: I wouldn't trust anyone who even suggests to use "a tool" for this.