I bought a used Ibanez 5-string that had some distortion in the signal. I replaced the guts of the bass with the Glockenklang 3-band stacked EQ and it now sounds AMAZING. Full, rich, sweet bass. No noise or hiss. It rocks and I love it - hence the 5-star review. But the install was... challenging. First, it comes with a wiring diagram and nothing else. No tips, no list of tools required. Not even clearly indicating which side of each component is the top side - rather important if you don't want to mix up the bridge and neck pickups! You should only attempt to install this if you have a basic knowledge of how electricity works. For example that the negative side of the battery is the ground. Or how an active bass power circuit is completed by inserting the 1/4" plug. And you NEED the following tools: Soldering iron, soldering iron holder, solder, soldering flux, soldering wick, tweezers to hold the soldering wick, wire stripper, scissors, a continuity tester to test for good connections and shorts, a clamp that can hold the things you are soldering. Sure, you could get by without all these tools, but you will not have a fun time. And watch at least 5 youtube videos on soldering tips first. Also, contrary to the photo, the product does not come with a socket for the 1/4" plug. It comes with what appears to be the cap of the socket, but not the socket itself. I have no idea why, but I used the existing socket so no big deal.
To the Glockenklang folks: It would be helpful to know the size of the pots in your product specs. My Ibanez 305 has 8mm diameter pots for all 4 knobs. The Glockenklang has 10mm for the stacked pot, and 7mm for the pan, volume and mid controls. So I needed to use a drill (with 10mm wood bit - more needed tools) to widen the hole. Also, my stacked EQ knobs were too large, so i needed to create two metal sleeves with scrap zinc metal around the low and high EQ controls. It works, but if you recommend new knobs, then make it easy for customers to order the right ones when they order the EQ. Or just include some simple ones like EMG does.
Also, the connections on the circuit board are incredibly close together. I needed to use 2 pairs of reading glasses to see what I was doing. A few extra millimeters of space around the connections that customers are meant to solder would make installation a lot easier, and short circuits a lot less likely.
Otherwise, rock on!