On Ebay their are 64mb PS2 memory cards and they are very cheap.  though I'm not sure If I can trust them because they come from China and look like the generic of generic stuff.

To find it just type in PS2 memory cards and look at the list that comes up. 

Could some one give me advice wether to buy this or not? 

Odds are that they are 64 Megabit memory cards, meaning they are still standard 8 Megabyte cards, just deceptively advertised. Gotta love communist china, First the Chintendo Vii and now this.

Claims to be 8 times bigger than regular card which means 64 megabytes.

Hmmmm... 

Nevermind about it being generic, after closer inspection seems that it made by same company as normal card (Magicgate) probably just manufactured very very very cheaply.

MagicGate is the trademark Sony (EDIT) gives the copy protection of some of its flash devices, including memory cards. MagicGate is not the name of the manufacturer, that is for sure. Wikipedia MagicGate

Give it a shot. Years ago I bought a non sony 32MB memory card. The only thing though is it wasn't picked up by the card reader that transfers ps2 game saves to ps3. If you're still playing ps2 and have lots of games then you do need more than the measly 8mb mc which fills up fast.