Screen printing T shirts in two colours with fine tonal dots and thin lines to register is not easy and requires skills and patience.
First, the artwork has to be right. Deciding on how to separate the colours from an original photograph can take some time. Getting the right size of dots when creating halftones for each colour separations depends on many factors and can be a case of trial and error. How much detail do you want? How fine or coarse is the silk screen you'll use? What's the size of the original and what size will the final print be? These are just a few considerations.
Then, there's the garments - How smooth is the fabric? Will the women's bamboo t shirts burn under the dryer under the extra heat? Are the sweatshirts too coarse to show the fine detail? Do you have the patience? Does your T-shirt screen printer need the hassle? Unless the artwork is right, probably not.