Any measuring system works when one is sufficiently familiar with it so as to be able to visualize the measurement and think in those units. For instance, If I tell you that someone is 6 feet tall, you probably have a good mental picture of about how tall that is, but if I say that he’s 1.8 meters tall you generally have no mental image at all. Likewise, If I tell you that it’s 21 degrees Celsius out side, you don’t know how to dress but if I say that it’s 70 degrees F you know instantly what to wear.
Besides the fact that it takes some getting used to, there are, in my opinion, two significant deficiencies in the metric system.
1. There is no metric equivalent for the the imperial foot. The existing metric units are either too big or too small for convenient use.
2. While this doesn’t actually effect every day use, Metric countries also generate electricity at 50 cycles instead of the 60 cycles we’re used to. This is completely silly because. even in the metric system there are 60 minutes in an hour, not 50, and 24 hours in a day. A circle still has 360 degrees not 300. back in the days of analog electric clocks, it was physically impossible to make an accurate one on 50 cycle current. It would run either too fast or too slow.