I've tried a whole bunch of menu bar ejecting apps, and Mountain is my favourite. I particularly like the ability to remount volumes, as Mountain has been able to remount volumes that even Disk Utility couldn't see.
Other things I like include notifications that when clicked will open the volume in the file manager I specify (in my case, I've chosen to use Path Finder), a skinny icon that doesn't take up too much space in my menu bar and dims when there are no external volumes mounted, and system-wide hotkeys.
I am still using Jettison in combination with Mountain, as Mountain doesn't yet auto-eject volumes on sleep (it can do it manually, and it can auto-mount volumes on wake from sleep). I contacted the dev to request this feature, and he says he has developed the feature, but wasn't satisfied with it as he could not figure out a way to notify users in case something when wrong when unmounting volumes. He says he will continue working on the feature, and I hope he is able to implement it as I would then have no need to use Jettison.