Pros
You pick your own days and hours. You can cancel 45 minutes prior to your shift. But these perks come at a cost, very low pay. After working for flex, you realize you can make more money working at CVS, or Safeway on an hourly basis and your car won't take a beating.
Cons
I deliver in the Silicon Valley so this is my experience. On most days, a "3 hour block" can turn into 4 hours or more, but you get paid for only 3. It's your fault if you go over 3 hours regardless of issues you encounter during your shift like you were given an incorrect address, no parking in or around apartment complexes, incorrect security gate codes are given, unable to reach a customer by phone, etc ... When you encounter an issue such as difficulty scanning a package, your only option is to call "driver support." The phone call takes 5 to 10 minutes and counts as part of your delivery time. By the way, driver support is "hit or miss." Sometimes, you get really helpful people, and other times, you get people that really shouldn't be working as driver support. It's a big minus! On a good day, which is rare, I can deliver all packages within my "3 hour block." On most days, however, a "3 hour" block is unrealistic because most of the time, you get 33-35 packages to deliver. That equates to 11 packages an hour. The average mileage is about 30 miles.