Grace creates, it's definitely a great learning experience! Doing the mysteries has helped me in two ways: I've learned easier ways of making units, and working with a large number of smaller pieces has helped improve my piecing skills through sheer repetition.
I guess how time-consuming it is depends on how fast a piecer you are. I'm slow so it's quite time-consuming for me. The mysteries usually involve smaller pieces with a lot of units to make. But it isn't necessary to keep pace with the mystery week by week. I think most of us end up finishing our top several weeks or months into the year. The main thing is to complete some of each clue each week so as to get the hang of how to make the unit.
I also have to shop exclusively on-line. Three of my favorite shops that sell 1/2 yd. are Fat Quarter Shop, Thread Bear Fabrics and Shabby Fabrics. Below are some of the shops I've found that will sell either a FQ or 1/4 yd. (Fabric Shack will even cut 1/8 of a yard, or they used to). :
Fabric Shack
https://fabricshack.com/cgi-bin/Store/store.cgi
Carolina Cotton Co.
https://www.carolinacottoncompany.com/shop.htm
Crazy Redhead Quilting
http://www.crazyredheadquilting.com/...htm?checkout=3
Feed Mill Fabric and Quilting
https://www.feedmillfabricandquilting.com/shop.htm
Ladyfingers
https://www.ladyfingerssewing.com/
L'il Red Hen
https://www.lilredhenquiltshop.com/shop.htm
The Little Red Hen
https://thelittleredhenonline.com/products
Mountain Creek Quilt Shop
https://www.mountaincreekquilters.com/shop.htm
Olive Juice Quilts
https://www.olivejuicequilts.com/shop-online.htm
Prairie Point Junction
https://prairiepointjunction.com/
Rossville Quilts
https://www.rossvillequilts.com/