I bought the K&F Concept NP-FZ100 battery set (pack of 3) for my Sony ZV-E1 and A7IV because I often do long shoots and photo sessions and don't want to be tied to the charger all the time. After several weeks of use, I can say: The batteries deliver very good performance and are hardly inferior to the original battery.

Runtime & performance
The batteries last a very long time, almost as good as the originals from Sony. With the ZV-E1, I use them for video recordings in 4K, and I easily get several hours of use - depending on the recording settings. It's a similar story with the A7IV, especially for photography, one battery is enough for a complete session.

Workmanship & fit
The batteries fit perfectly in both cameras and in the charger. No wobbling, no problem with detection - the camera shows the battery level correctly. This is important because some third-party batteries sometimes have problems here.

Price-performance
For the price you get three batteries, which is a real bargain compared to the Sony original. Sure, Sony batteries are probably slightly better in terms of efficiency and lifespan, but if you film or take photos a lot, you'll be absolutely happy with these.

Conclusion
If you're looking for a cheap but reliable alternative to the original batteries, you can go for this one without hesitation. Long runtime, no compatibility problems and great value for money. I'll definitely get some more if I need them!