Tried those first but no, they didn't work great with the data I was able to extract; those datasets are only handwritten digits which apparently weren't close enough to the computer printed ones.

I think the artifacts from the square borders (eg if it's slightly mis-cropped or misaligned) were also tripping up the model before I had my custom dataset loaded in there.

Edit: I should say this was my first stab at doing machine learning so I may be missing something; definitely open to ideas or suggestions!