I'll second the opinions expressed by Eddie and lawajava. If by "mastering" we're talking primarily about limiting, then
nothing beats Ozone for the novice-to-intermediate user. Even the advanced user will appreciate its ease-of-use and fast, consistent results.
In terms of price, AFAIK Ozone is still $200. Less than Fabfilter Pro-L but more than Voxengo Elephant or Meldaproduction's MDynamicLimiter. Ozone may be the senior citizen of mastering plugins, but dollar-for-dollar, it remains a good value. Especially considering how easy it is to get good results without having the first clue about what limiters really do. Ozone's limiter can be severely abused before it destroys your mix, can be driven into the red without distorting, and will never alias.
Mastering involves more than just limiters, and all of the aforementioned competitors are just limiters. Ozone also gives you a great harmonic distortion module (better than Saturn on full mixes) and multi-band compressor included in the price. MDynamicsLimiter does have harmonic distortion and Limiter No. 6 has its clipper, but neither is in the same class as Ozone's exciter. Ozone also has the stereo-enhancer, often maligned because you can do damage with it, but still the best I've ever used (just apply it lightly if at all). And of course you get a pretty good equalizer that can do M/S, linear phase and spectrum matching. That's a LOT of quality functionality in one $200 plugin!
But here's what Ozone lacks and Meldaproduction plugins do extraordinarily well: dynamic equalization. Here at Casa del Bit, MDynamicEQ has permanently retired two of Ozone's modules: the EQ and the multi-band compressor. It's usable on both tracks and busses for a variety of tasks from basic equalization to compressor-type applications such as ducking, leveling and 2-bus glue. Even if Ozone could do all that it's too demanding on the CPU to have many instances in a project.
MAutoDynamicEQ is a lot of fun for spectrum matching, but IMO non-essential. It's a feature I use mostly as a sanity check on full mixes. Same for Ozone's spectrum-matching feature. There is no benefit to having both MAutoDynamicEQ and MDynamicEQ. If you don't desire the spectrum matching,
grab the latter *RIGHT NOW* as it's half-price ($46) for today only. Personally, I would not buy the Meldaproduction mastering bundle. There are too many redundant plugins. As dubdisciple pointed out, MDynamicEQ isn't needed if you have MAutoDynamicEQ. The bundle also includes MAutoEqualizer, which does offer linear-phase but otherwise is essentially MAutoDynamicEQ without the dynamics
There are also two limiters, two non-dynamic equalizers and two broadband compressors in the bundle. The multi-band compressor is, IMO, also redundant alongside MDynamicEQ. (I just see no need anymore for multi-band compressors now that I've seen the light of multi-band dynamic equalization.)
There is, however, one ultra-cool plugin in the bundle that Ozone cannot match:
MSpectralDynamics. It's hard to describe what this plugin does because there are so few products like it. But I can tell you that it's become a standard part of my process for 80% of my projects. And it may be only 80% just because I don't understand it well enough yet to make it work the other 20% of the time. Watch for my detailed review in the September issue of SoundBytes.