Pre-release tests of handheld devices by the V Society have shown that in some games, the loading time of micro SD cards is almost the same as that of SSD SSDs. If users use a high-capacity SD card, they will hardly notice the difference.
Both "Canada White" Linus and tech video channel The Phawx tested on steam Deck and found that micro SD and SSDs had nearly the same load times in games like Control, Dead Cell, and King of Fighters 5. In some cases, the micro SD's loading time is only 2 seconds slower, while others the test speed is exactly the same.

Portal 2 and Ghostwalker are about 10 to 17 seconds slower on micro SD, so actual results can vary greatly depending on which games proton software and Steam Deck hardware compatibility. Currently, V-Club only allows testing of a few games, and Steam Deck's software is not yet complete.
In the dismantling video of the V Society, the official said that even if it is completely feasible, it is not recommended that users replace the internal SSD themselves. The official in the video said: "Our SSD is very close to the wireless module, has been specially selected and tested, and does not interfere with Wi-Fi and Bluetooth." ”