Yeah i have used a 300X with no problem, worked fine until the card like so many other cards/brands went into read only mode.
But it could be a incompatibility issue with that camera brand/model and the X300.
In general a dashcam write 3-4 MB every second at most, meaning even pretty old SD cards should be usable too, i have at times used old 4 Gb cards to update firmware on dashcams.
A 600 - 633X card will have write speeds around 30 MB every second, making it plenty fast for any of the current dashcams on the marked.
Of course a fast card is more enjoyable to work with on the computer if you are moving a lot of files of it at once, but if you only grab 1 or 2 files now and then for youtube uploads like i do then the really fast read speeds dont matter much in the big picture.
Then again - again, there is little to be saved buying a slower card, unless of course you are buying the really fast class 10 - U3 cards that have write/read speeds over 80 MB/second.
But U3 cards are wayyy overkill for all dashcams, even dual camera systems where 2 cameras are saving files on the one memory card.
Too bad you are not near me, cuz i have a slew of cards we could try out in that camera to see what it like and dont like.
If i was you i would try to borrow just about any SD card to make sure it is not the camera before you go invest in a new memory card, even small old class 6 SDHC cards should be able to work with the camera of yours.
But for shopping you will of course have to look for more recent class 10 - U1 SDXC or SDHC cards.
Buy in a local store or fulfilled by amazon, i had amazon cards fail me and they almost have a new card in my hands before i have been able to ship out the broken one at their expense.
Your local Canadian warranties might be even better than the default 1 year global, we Danes / EU boys enjoy 2 year warranties on most things.
Myself i have good experience with Lexar - Toshiba - trancend - kingston - PNY.
I have had a lot of kingston cards fail me too, but it take me 3 minutes to do a online RMA and 5 minutes at the most at the shop waiting to get a new one, i think its just a matter of numbers cuz i had just about all other brands fail me too at one time.
Only sandisk is in general warned against for dashcam use.
