Give a quick search for PS2 Memory Card and sure enough, you’ll find convincingly OEM memory cards from all sorts of providers. After not using a PS2 for the past three years prior I thought nothing of it and bought one of these, just assuming the technology has moved on since I was last part of the PS2 scene.
Only after spending time on the homebrew communities did I find what the secret was of these large memory cards was. While some are or appear to be genuinely what they say, there are some warnings against third-party memory cards.
This is always a speculated topic on the matter (please let me know otherwise). Some cards use a technology called compression to achieve more storage on similar hardware. Compressing data is (in the case of a zip file) when parts of data which is similar to other parts in a container are merged, Simlarly some of the cards will try and compress the savegames so that more can fit on the card. While this isn’t an inherently bad idea, this will cause the system to slow down noticeably, and the higher the storage amount of the worse performance will be. Most games will take this on the chin (Sims 2 is slow on an official 8mb, with a high capacity be prepared to wait a long time), but means the ‘do not remove the card of turn off the console’ space of time is extended for a long time.
You have to bear in mind that while Sony has a strangehold on the Memory Card copyright, it does still mean that the PS2 memory cards and manufactured to the highest quality with pretty heavy restrictions before being accepted to sell. Contrast this to a Chinese developer who does not have the same financial backing or reputation, so it is very possible to end up receiving a duff card from the merchant.
If the circuits inside the memory card have been constructed without following guidelines, something simple as a missing hardware feature can cause the system to corrupt the storage medium. When a memory card is corrupted, it can only be repaired by reformatting the memory card. This wipes the card clean, removing all the broken data off and leaving it ready for new content.
Go for it. In my personal experience, I have had no issues with one of the unofficial memory card losing data, but the experience of saving games to it was less than ideal. These cards do not go through extensive testing as the official branded ones do, so it pays to be cautious as you may be given a duff card, in which case it is handy to keep official Sony memory cards for backing up those all important save files.