Safety pens those with retractable nibs enjoyed a rather brief period of popularity in the US and UK, and even now few anglophone collectors would think of making regular use of one. A different attitude prevailed in Germany, Italy, and especially France, where safeties remained popular up through the 1940s.
In any event, three advantages peculiar to safeties deserve notice. First, the pen seals more tightly than any other; second, since the nib remains immersed in ink when not in use, it can be used with India and other drawing inks that would hopelessly gum up just about any other fountain pen; third, since the ink chamber is opened to the air each time one uncaps the pen (extending the nib seals it once again), a safety is largely unaffected by changes in atmospheric pressure between uses.
If you want to use a safety, make sure that it has had a fresh seal installed by a qualified repairman. Many sellers will briefly test a safety and then aver that its seal is good, even though the ancient cork seal is likely to fail within a few days if subjected to regular use.
NOTE: Not long ago, newspapers reported a French farmer's discovery of the long-buried remains of a WW1 soldier. The soldier had been carrying a Waterman pen that amazingly enough was still full of ink, and which still wrote, right out of the ground. This was, and could only have been, a retracting-nib safety pen.