I picked up Private Reserve Sonic Blue on a whim. A year and a half later, I still don't know if I like this ink. But I'm going to review it anyway!
Sonic Blue is in the Blue-Black spectrum, though I'd call it more of a blue-grey. It lacks any special properties like water or UV resistance. It doesn't dry particularly fast, either. It has mild shading - as always, very dependent on the nib & paper.
Private Reserve inks are a solid deal, as far as volume to dollars. Typically, a 66ml bottle will run you eleven bucks. I think that's a surprisingly good ratio for a "boutique" ink. That is, if you actually like the ink.
Unfortunately, Sonic Blue suffers the same flaws I've found in my other Private Reserve inks. The formula seems to be very watery and, whether directly the cause or not, there are several issues. Sonic Blue is very inclined to dry on the nib; any pause in writing can result in a hard start. SB also has a tendency to stick in the converter, leaving an air pocket between the ink and feed. The flow is bad, both when traveling through the pen and also betwixt nib and paper. The ink offers no real cushion for the tipping to glide. SB does not play nice, but at least it doesn't eat your pen or feather everywhere.
Ultimately, I like Sonic Blue in spite of its problems. I don't use it as often as my more agreeable inks. I have to be selective about which pens I use it in or performance falls below a tolerable threshold. But I still use it - often enough to be halfway through the bottle.
If you're a fan of greyish blues and don't need the water-resistance (or smell) of Noodler's 54th Massachusetts, then this ink might be worth checking out. For best results, I recommend using it in a self-filler with a well-tuned nib.