Sony 18-105 f4 PZ lens is one of my most used lens for sony a7s. It does not have the best image quality. But it has many advantages over other lens. Here are some facts about this lens. You won’t read them on product description. Only people who have used it extensively knows.

1. it has very smooth zooming in and out effect just like traditional camcorder.
2. you can change the speed of zooming by how much force you push the zoom lever. I would say you have 4 levels of speed.
3. this lens is parfocal. very nice feature.
4. it has amazing image stabilization. like camcorder. I can handheld walking with this lens. it is like I am using shoulder rig.
5. the manual focus ring is the worst I have used. It is focus by wire. but it is the worst one. I have used Panasonic lens which are also focus by wire. I also used some other sony e mount prime lens which are also focus by wire. They all behavior much better. Just forget doing manual focus with this lens. I would say this is the major downside with this lens.
6. color, contrast is not that great. I can feel this lens produce a bit flat image. For low budget and running and gun style of shoot. This lens is my favorite. But if I am looking for the best image quality, I switch to prime lens. not because of the sharpness but for the color rendition, micro contrast kind of characteristic.
7. Internal zoom. Does not change length when zooming. good for using with matte box.

Overall for $599, this lens is definitely worth ownership. Do not move away because it is aps-c only. I use this lens most of time on a7s. It is so convenient and versatile.