Flexible Panels are lighter and you can get them also with high efficiency.
During driving we should usually use the engine power for charging. So there are not much need for using solar while on the way.
All panels can gain much more power, if they are directed to the sun.
The question should be more, if you want to mount a fixed panel, or if you want to use a mobile solar panel, which you can put in the direction of the sun.
Any Solarpanel drop most of the power, if parts of the panel are in the shadow. So consider that too, if you still think about to mount it fix at sample to the roof, where maxtrax or roofbox can bring shadow.
Also consider that you have to park into the sun, when the panel is really mounted. At hot days you probably prefere more shadow...
A good flexible 120W panel can fire a compressor fridge, Notebook, Camera easily - if used with a good solar charger and battery without the need of other power sources, just a week of rain and no sun - can bring the need of the 12v power of the car.
I did go a mixed way, a small 50W flexible panel mounted, to get power for extended parking of the vehicle - during overlanding I can take the 120W Panel under my matress for more juice.
Maybe you find this helpful:
Fixed Solar Installation:
https://www.4x4tripping.com/2020/04/...efahrzeug.html
Mobile Solar Example:
https://www.4x4tripping.com/2020/06/...laranlage.html
The mobile Version is very light an tiny - but is less powerful compared to a setup with good components. As the Video tells - it stilll works good enough for most purposes...
Flex or nonflex Solarpanels - both can work well... For both there are Panels with bad values (efficiency) available.
This flexible EFTE Panel powers a lot with just 50W
https://www.amazon.de/gp/product/B07...d537947d2ec310
On sunny days this is enough for Fridge/Smartphone/Notebook - and costs under 100 Euro. EFTE brings a lot, if you panel is not directed to the sun. It powers the same power than my 120W non EFTE Panel - when both are not directed into the sun.
Surfy