It would depend on what kind of quilts you make. I don't like the 9" because you can't cut 2 - 5" squares. If you use 4 1/2" squares then they might be good. If you like paperpiecing they are good because you have a lot of variety. The layer cakes are good because you can get 4 - 5" squares out of them. The pre-cuts are great for quick projects, like table runners, potholders, etc. Just think about how you use your fabric.

I sometimes buy FQ when they are on sale & once in awhile a jelly roll or charm packs. Mostly I buy yardage. I think the fat 1/8 would be just too small for me. I probably wouldn't buy them.

i don't usually buy less than 1 yard of anything unless it's a remnant. Nothings worse than putting together an idea and not having enough to fill in the design.

I have consistently found that all FQ packs are not cut at 18 x 22 - squaring them up will result in loss of fabric. If you try to square up a fat eighth, I would think it would be more frustrating. I believe that patterns developed for FQ, jelly rolls, layer cakes, etc. allow for a little wiggle room.

I love the precuts, I save money by not buying extra fabric that I don't need. I might buy them if there was a theme to them (candy, fruit. etc). It also depends how many fat 1/8th to a pack. For the most part, I doubt that I would buy them like I buy jelly rolls, charm packs and layer cakes.

A fat eighth is 9 x 22 so if you are a scrap quilt lover they are nice, more than a layer cake but less than a FQ and a sample of each fabric in a group. Left overs will usually go with other groups from the same maker. I like them for scrappy or applique but have to buy extra for borders or background. To each his own.

This is also the way I feel!

Made a wonderful lap quilt using Moda charm packs. I do occasionally get FQ as I have a pattern that calls for FQ but I also cut my own FQs from yardage.

Buying fat 8th depends on what kind of quiltmaking you do.
If you are looking for lots of different colors and designs for more scrappy quilts then they work. But to me, they are useless for 99.99% of my quiltmaking regardless of the cost. Then you can always give them to a quilting friend and let him/her worry about using the smaller pieces.

I love precuts--but an 1/8th wouldn't be on my wish list...I would just get the quarters--and use the extra for something else.. :)