I have tons of experience with this stuff. I designed, built and sold several types of piezo and mag preamps, so here's the $1,000 question: how long do you need your guitar cable to be?
A guitar cable has capacitance (roughly 35pF/ft on a good quality guitar cable, like the Mogami brand, etc.).
The cable's capacitance interacts with passive guitar pickups, both the magnetic and the piezo type.
Piezo pickups have much higher impedance than the magnetic pickups and most of them also output lower signal levels, so a few things are going to be noticeable right away when using a longer cable with a passive piezo pickup:
- The high end of the frequency spectrum will start to roll off
- The sensitivity to external noise sources (fluorescent lights, dimmers, etc.) goes up
- On some cheap guitar cables, because the source impedance (the piezo pickup's impedance) is so high, you will start hearing noises whenever you move or touch the cable (mechanical noises will make it into the audio path)
A preamp or any active piezo system will get rid of the cable problems, but if you're using a piezo system with a good quality cable of a relatively short length and you play mostly at home or in a studio, you can get a very decent sound without the use of an active system installed in your guitar or a dedicated piezo preamp.
On the other hand, if you're playing on stage or on a venue with lots of noise sources around you (stage lighting system, etc.), I would recommend either an active system or at least a preamp on the guitar cable.
Also, note that there's a big difference from one piezo system to another. Based on my experience: cheaper bridges may or may not work well, it's always a hit and miss, but I always got better and more consistent results from brand names (Fishman, LR Baggs, RMC, Graphtech Ghost bridges, etc.).
I used to buy the cheaper ones from Aliexpress, even built my own transducers for while, etc., but in the end I gave up on doing this, not worth the effort. These days I'm only using high quality bridges and I design and build my own preamps and active systems. In my opinion, a good quality piezo bridge is well worth the money, regardless of how you're going to use it (passive or active).