Yeah, I've used it for a long time. It's popular for a reason, Ozone is pretty damn good and it's a kind of one-stop shop for all your mastering needs.
Do you need it? Nah, not really. It doesn't perform magic other plug-ins won't. But it's handy to have everything in one place, working well with each other, well documented, unified interface and all of that.
I'm selling mine, actually came here to put an ad up.
As a bundle along with Neutron and some other Izotope goodies. Not because it's not good but over time I've just found replacements I prefer working with.
They're also more expensive so something's gotta give!