It won't make you play better, but you'll sure sound like it.
Having had the 18V mod for quite some time in my LTD EX-401 (EMG 81/60), I've found playing with the standard 9V setup to be lackluster.
I had bought a Gibson Explorer outfitted with EMG 81/85's and I had always wanted to mod them, but it lacked the cavity space for the extra battery.
Lo and behold, this product solved my dilemma. It's actually pretty damn clever.
Now, this will not make your guitar louder. It will not make it gainier. It will not make your male pattern baldness grow back.
It gives your pickups signal more headroom, which gives it better dynamics. It's one of those subtle changes that can affect your tone in a big way, like changing your strings, using a different pick, etc.
EMG's signal is compressed right out the gate. This "decompresses it" and gives it more presence.
Look at a graphical representation of a wavelength, like what recoding studios use on their computers when laying down a track. Let's say the peaks of those waves are limited by the output of the guitar. With stock EMG'S, it's 9V. When you push more voltage through, you're raising the maximum "ceiling" to where those peaks hit. That's called "more Headroom". The waves will be broader with bigger range, and won't have such a "squashed" sound.
It the EMG manuals, they encourage experimentation, and explain the limit their pickups can handle is 27 volts. This product is under that threshold, so it is safe to use.
I have since bought a second battery pack for a LTD EC-1000 (81/85) I recently acquired. I love this mod so damn much. All the claims on the package of the 24volt Mod are true.
My only complaint is they are a bit pricey. But I have no problem helping support a small business. I'd rather my cash went to them instead of Guitar Center. They did ship extremely fast and it was free.