It's not like the "Michigan Left" (I hate that name, "Metro Detroit Left" would be much more accurate) does away with making a left turn at a light. Instead, you make a right turn at light at the intersection, and then a left turn at the extra stoplight they added for the Michigan left. The only time it's really a win is when there's no traffic on the road you're crossing, so you can turn right on red and then left on red. And of course, in that case it would be easy to turn left on green if it were a normal intersection...

These aren't unique to Metro Detroit. Portions of the East Beltline (M-44) in Grand Rapids, one of the busiest streets in the area, make use of the Michigan Left.

Depends on how busy the intersection is. Worst case scenario:

Miss the first light to cross straight through the intersection. Idle.

Queue into the non-intersection left turn lane to cross two lanes of oncoming traffic. Idle.

Wait for a right turn red light and idle, or wait for an opportunity to merge into two lanes of oncoming traffic and idle.

The best case scenario is light traffic and hitting both lights green, but you're still going further and taking longer to accomplish a left turn signal's best case scenario. A double left turn lane with signal is almost always faster in my experience.