I get my sd cards, etc, from Wilkinsons.......good price and local.
My son in law has just finished a digital photography course, in the local Art College(Plymouth). He was told that 32 gb cards are unstable, and not to use them for really important work, 16gb were recommended as stable and no worries to use.
I only use 16gb cards in my digital camera having been given that advice.
So if you are using this in a medium priced dash cam, you do not want to run the risk of a corrupt file, if your claim depends on it. As the cameras spool through and re record anyway, then 16 gb should be mote than adequate.