Are Quill Stems Safe?

Both are 100% safe. A threadless setup is easier to adjust if your headset becomes lose mid-ride. A quill stem is easier to adjust bar height mid-ride.

Are quill stems dangerous?

Condensed answer: Quill stems aren't inherently bad and have proven themselves over the years. However, they require a heavier steerer and a more finicky headset. They also limit the number of forks that you can use and create a necessity to sell forks of different sizes.

Should you grease a quill stem?

Compression-Slotted Stem

Center the bar in the stem, which you should already have inserted. If necessary, open up the compression slot as you did during the removal process. Apply grease to the compression slot bolt and install it, but do not tighten it fully.