I thought I could live with a slow spinning drive - I couldn't...
The replacement went without a hitch. I was dreading some kind of hiccup along the way, but the directions were so clear and detailed, I knew what to expect at each step. So in the end, I was able to successfully replacement my stock 500 GB 5400 RPM hard drive with a 128 GB SSD, and that has made all the difference.
I went through this process once before on an older, probably 2012 era, Mac Mini. I did so without instructions like the ones provided by iFixit. I accidentally severed the a cable that went to the fan, so after my repair and had a non-working fan. This is why I was so nervous about this replacement. But thanks to iFixit, all went well!