Is it worth upgrading my SSD card on my mid 2010 MacBook Pro?

Like the others have said it won't make any difference.

However, make sure you have the MX300 has the latest firmware version since there was a bug with several early versions of the MX300's firmware which could cause the SSD to have issues (it would not reallocate bad blocks for one). It has been ages since I did a firmware update for the MX300 SSD so I don't recall if the later .iso firmware update files are Mac friendly for creating a bootable USB firmware updater. I believe the version which fixed this issue had "70" in the firmware version number so it is best to have at least this version of firmware. If the SSD is not running the latest firmware, then use the downloaded .iso firmware updater image as a source for Etcher (Mac/Windows/Linux) to create a bootable USB firmware updater (hopefully).

You won't see any performance difference between them. Your bottleneck is the interface with the Mac's logic board.

You'd be better served by getting more RAM for your Mac than a slightly faster SSD. https://eshop.macsales.com/shop/memory/Apple_MacBook_MacBook_Pro/Upgrade/DDR3

And even then, I don't think it's worth it to sink any more money on a 13 year old device at this point. Save it, and use it to buy a newer Mac instead.

<< mid 2010 MacBook Pro, 8GB memory >>

upgrade to 16 GB and it will seem MUCH more responsive.

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