Time for the impedance matching lecture for newbies. I'll try not to get too technical. It is the nature of piezo pickups that they need the input impedance of the next device in the signal chain to have a 1 Meg ohm input impedance. All soundboard transducers like the K&K mini and all undersaddle pickups use piezo crystals to turn vibration into and electrical signal. Run into a typical mixing board of around 800 ohms, the signal is bright and harsh. It is how piezo pickups react with the next device that determines the frequency response. With acoustic instruments, the first devise could be a pre, a DI box, a mixing board or an amplifier. You need something to match the impedance so you sound good. Virtually all acoustic pres and acoustic amps have the correct value input impedance. Some DIs do, some don't. Some mixing boards have a switch (labeled hi Z). If your guitar has a battery, it has an onboard pre amp so you are good to go. Regular electric guitar effects boxes and amplifiers usually don't match.
Some well known quality devices are the RedEye, the Baggs PARA DI, numerous Fishman products, K&K, etc.Usually money buys mo bedder. I am fortunate to live by Teddy Randazzo, maker of Dazzo pickups. I have them in six guitars. I have six and twelve string Pono parlor guitars. They are identical in every way but the number of strings, but they have different pickup sets tailored to each guitar. The K&K is designed to sound good in the most variety of guitars. It is this compromise that necessitates a lot of EQ. With Dazzos I use little to no EQ. K&K is the one size fits all solution, and maybe the way to go if you are not a sound geek.
Sometimes I think those that sell and install pickups don't want to lose a sale by pointing out the need to buy more gear. I can attest to the lack of this basic knowledge because I co host an open mike. 95% of K&K owners think they can just plug in, and they can if they want a harsh tone. It got so bad I had SunnAudio, another fine local company, build me a DI box we plug everyone into. Now those $4000 K&K equipped guitars sound good.