Sand Hour glass by Raisons Overseas. had some strong characteristics. On the positive side, it was far simpler and cheaper than the mechanical clock or the earlier water clock. Resetting it after it ran down couldn't be simpler. And it didn't vanish when you used it, the way a graduated candle did. It's accuracy wasn't bad either, once some problems had been solved. You couldn't load just any old sand into it. You had to find a free-flowing material that was unresponsive to humidity.

On the downside, sand hourglasses were pretty short-term timepieces. The very name tells you it's hard to find one that'll run more than an hour. The other big drawback is that they can't be calibrated. Sand moves downward in jerks. The edge of the sand is uneven. If you mark five-minute intervals on the glass, the sand will hit those marks differently each time you turn it. An hourglass really tells you only when an hour is up.
Hourglasses found their place in setting off blocks of time. The time between canonical hours in a monastery, or between watches on board ship. Of course, they didn't run long enough or accurately enough for marine navigation. They were a poor man's timepiece -- a kind of clock for everyman.
Both the mechanical clock and the sand hourglass found powerful symbolic roles during the Renaissance. The complex mechanical clock with its rotary gears became a metaphor for the heavenly spheres or the wheel of fortune. But the hourglass, whose sands run out, became a metaphor for that running-out-of-the-sands that we all inevitably face. It became, and it remains, a universal symbol of death.