Sometimes a manufacturer forks v4l-dvb all on their own and writes a driver for their device so they can claim Linux support.
1. You might get well support for your device
2. If the manufacturer provides open source drivers, volunteers are able to provide long term support and submit it to the Linux Kernel.
1. If the manufacturer provides binary modules, or object files you might have to recompile the 3rd party driver every time you update your local kernel version. Compiling might require some additional dependencies (eg. linux source tree, specific toolchain for particular architectures etc. so it might not be so easy to install them everywhere
2. If the manufacturer stops updating the drivers you might loose support for those drivers on newer Linux systems
In case a manufacturer provides open source drivers the patches can be sent to the linux-media mailinglist Linux-Media Mailing List (LMML)
1. Generic over nearly all Linux versions starting from 2.6.15 on
2. No recompilation needed if you update your kernel version
3. Manufacturer might provide well support for the device you bought
4. Drivers can be profiled easily and more accurately than in kernelspace
5. If the driver crashes your system won't be affected
6. If the manufacturer would stop to support the drivers, the application driver will still continue to work with newer Linux systems since the Kernelspace <-> Userspace interfaces are fixed and are not meant to be changed
1. this is only meant for hackers that they won't have insight about what the manufacturer is doing, regular endusers usually won't cope with device driver sources anyway