As a singer-songwriter guitarist who records and mixes at home, I've had the chance to use Pulsar Modular's P440 Sweet Spot. It's designed to be a mastering EQ, and here's my take from a hobbyist perspective:

What is it?
The P440 Sweet Spot aims on providing smooth, musical curves and a "sweet spot" that makes it easy to dial in pleasing tones.

What I like:
* Musical EQ curves: The EQ points and curves are very musical and forgiving. Even with larger boosts or cuts, it's difficult to make things sound harsh or unnatural.
* Ease of use: The interface is clean and somewhat intuitive. The controls are responsive and offer a good range of adjustment. It's a plugin that encourages experimentation, and I say this in bold letters, as it took me a better half of a year to fully understand everything that it can do. The latest addition of the EQ band visualizer is amazing, although I wish it had a spectrum analyzer as well.
* "Sweet Spot" focus: The plugin lives up to its name. There's a certain "magic" to the way the EQ interacts with the audio, making it easy to find pleasing tonal balances.
* CPU friendly: It's relatively light on CPU usage, which is always a plus for home recording setups.

How I use it:
* Vocals: I find the P440 Sweet Spot great for shaping vocal tones. It can add air and presence to vocals without sounding harsh, or add warmth and body without sounding muddy.
* Acoustic guitar: It works wonders on acoustic guitar, adding clarity and definition or warmth and fullness as needed.
* Electric guitar: It's useful for shaping electric guitar tones, especially in conjunction with amp modeling plugins. It can help refine the overall sound and make it sit better in the mix.
* Bass: The P440 can be used to add some subtle warmth and definition to bass lines.