My 2014 1.4ghz 500 gb 5400rpm HD Mini has been slow from the start and only got more so as the years went on. Rather than buy a new machine, found a Samsung EVO 850 2.5" at $130 for the SSD and $35 or so for the iFixIt tools and voila.
Ordered a USB to SATA cord for $15 from Amazon and connected the drive. A little tricky formatting it using DiskUtility, etc. but eventually got the hang of it and restored it using TimeMachine from a saved disk image. There was likely a faster way, but this worked overnight. Tested the disk first via USB and the machine was already like night and day: all functions were instant, including a reduction of boot up from c. 2 minutes to c. 30 seconds. Opened it up and the results were event better. The still photos on the guide/site covered every step and my 11 year old daughter scrolled from step to step on the guide, immediately able to ID all parts (even the microscopic Apple security torx screws) in second. Excellent results. Went from 45 or so megs per second read/write to about 500. Like a new machine... for $160. Could not be more worthwhile.
Order the identified tools from the guide. They got here in 4 days-- THANK YOU. They make the repair much easier/possible, especially the tiny security torx screwdriver (maybe Home Depot carries them but darned if I could find them) and the logic board tool-- the idea of improvising that tool to dislodge the logic board seems silly and maybe risky. Also, my advice: figure out a better way to clone your drive than Time Machine, which was endless and failed at least once for no discernible reason. The only improvement on the site (and apologies if I just could not find) would be a better walkthrough of the steps one needs to take in the Mac OS to prepare for this repair as an upgrade from the existing HD. Otherwise, this was simply an excellent site and service. THANKS.