I think so for peace of mind more so when you're not home. What's also nice about the nests is they interlink (communicate) wirelessly so any existing hardwired units can talk with additional battery units; if you wanted to add elsewhere. They're smoke/co and you have no choice otherwise so your existing setup with just smokes in the bedroom and smoke/co in common areas is even 'safer?'.
I think so for peace of mind more so when you're not home. What's also nice about the nests is they interlink (communicate) wirelessly so any existing hardwired units can talk with additional battery units; if you wanted to add elsewhere. They're smoke/co and you have no choice otherwise so your existing setup with just smokes in the bedroom and smoke/co in common areas is even 'safer?'.