Incredibly useful, subtle, smart
I'm sure there's something but can't think of anything at the moment.
I've been using Boomerang for much longer than a year, that's just the longest option this allows me to choose. I use it every day and am still probably underutilizing its capabilities. With it I have been able to be on top of follow ups, handle emails when top of mind but make sure they go out at a more optimal time for response, and with Inbox Pause... Catching up after OOO has been so much easier.