The SanDisk Ultra Fits do get very hot when you write a lot of data to them at once. That's probably the biggest complaint about it. Every time you write data to flash memory, it heats up a little. So the faster the flash drive can write, the hotter it tends to get.
I have the 64GB version. It gets hot enough that it's uncomfortable to touch, but not so hot that it burns my finger. Other flash devices can get hot enough to boil water.
https://www.youtube.com/watch?v=3hhdWwvh5kI
I keep the Fit because of its great performance for its tiny size. But I can understand the heat being an undesirable feature for some people. I haven't had problems with it in over a year of use (I dumped some games onto it, before I upgrade from a 128GB SSD to a 500GB), so the temperature does not seem to affect its reliability.