Coming from a gi background the heel hook strikes fear in the hearts of those not used to the technique and I believe that this move and other leg locks are a large part of why many gi practitioners don’t venture to try training no gi.
The collar sleeve position is a great starting point for setting up your attacks from your open guard. Super effective for setting up the omaplata and triangle as well as some of the newer movements such as the berimbolo, farside collar sleeve, and matrix style attacks.
Developing a guard game no gi is not easy. Especially for athletes crossing over from gi jiu jitsu with the abundance of grips. Since we are limited in our grips in no gi we have to make full use of both our upper and lower body. This might also explain the usage and acceptance of lower body attacks in no gi.