I use the top slit needles when I accidentally have a thread break -- I take out half a dozen stitches and then bury the thread. i have enough troublr threading a needle with new thread -- used "frayed" thread is impossible on a size 10 needle.
Besides, I have to use a needle threader a lot. My eyes were never that good -- and with age (who me???) they haven't gotten any keener
Mim