I only ever sold one Intel NUC which seems to have run into severe stability issues in less than three years. Perhaps my experience is an outlier?
One issue I definitely have with it was that in order to clean out the HSF (fairly standard laptop HSF design, got clogged with dust in about 2 years in an office environment to the point that the CPU overheated), I had to open the NUC from the bottom, go through where the 2.5" SATA drive would be (I used M.2), remove the motherboard through a tricky "angle it just so on one side" affair, all the way through to the top end of the NUC. It wasn't fun, and I'm pretty sure the designer could have allowed the option to take the top off rather than having to take the whole thing apart, not to mention adhesive bits that would no doubt need replacing once the NUC has been opened a few times.