Sorry, could anyone enlighten me on the "Avoid ElGamal" part? I thought it was pretty secure. Is it due to bad efficiency?

I would guess the author wanted to say "avoid cryptosystems that work over Z_n ring", especially that you will use ElGamal when signing or encrypting over elliptic curves.

It is fine, but a good reason to avoid FFDH, RSA and other algorithms over multiplicative groups is that you need longer parameters compared to ECC.