Setting up a new C7 hub. Trying to do a minimal install i.e. one or the other. Any reason to use notifications and HSM? Does HSM have a lot more overhead than notifications? I'm aware of the differences between the two, just not what they require of the hub.
I'm not sure there's a good way to compare; either should basically sit and wait for events, do its thing, then go back to sleep. (Similar to most apps.) Hub impact should be minimal either way. I'd personally choose the app that I think is best suited for the task, which for me would be HSM. Your preferences (and needs) may vary.