Pros
Flexible scheduling is nice - able to request time off and adjust what times of the week you are able to work. it used to be that only an average of 17 hours per week were needed in order to qualify for health insurance. Once ObamaCare went into effect, Trader Joe's decided employees could get just as good coverage for the same price or less through the ACA, so increased the number of hours needed to 30 in order to qualify. This was a very poor move on many fronts in my opinion. Your experience working at Trader Joe's will vary drastically based on the location and weekly sales of your store as well as what the captain is like and the people he hires.
Cons
If you are not able to have "open availability" you may not get all the hours you need. Open availability means you do not have any restrictions as to what hours you can work -- which is as early as 4a.m. all the way to 11 or 12 at night! Being able to request time off when you need to or change schedule due to school or something is probably why there have to be a lot of employees so there is somebody to take your hours when you need to attend to other things.