The free app is all that you need for basic monitoring. It also does not flog your data allowance.
The paid Nest Aware with continuous recording does flog your data. Assuming full 1080p, it can be up to 30GB per hour – you will need NBN unlimited for that. It will also hog upload bandwidth – now that is not an issue for downloaders, but multiple cameras may be an issue.
On that point Arlo and now D-Link use a separate Wi-Fi base station – the latter allows for local recording as well. I am yet to be swayed either way, but it does make sense to keep major traffic off the Wi-Fi home network.
Still, the Nest buyer will want all that Google offers and it does that via Wi-Fi.
And don’t be too concerned about reports of Nest hacking. The problem is you – don’t reuse passwords, especially those generic ones you use for everything. Better still use two-step-authentication.
Overall without Nest Aware and local storage all the devices as an ecosystem score 4-out-of-5. If you can afford Nest Aware (and Nest gear) then its 5-out-of-5