I have done a McKenna Ryan kit and as her patterns call for dozens of different fabrics I think it works out much more cost effective as some of the pieces are only 2" square and I would have to buy at least a 1/4 of a yard as that what most people have as a minimum cut.
I suppose it would depend on the kit.

I bought a bunch of kits from fabric cafe. Their sales are great. Each kit has a pattern and 3 yards of fabric the quality is good. At the time I bought them they were on sale for 14.99. the sale now is 19.99 ea.
Now I know I can buy 3yd of fabric, use the pattern and have a top. lso if you want it larger just add bigger border,You;ll need fabric for that.

I have a made a wall hanging from McKenna Ryan and the fabric was great. I bought a kit from Joanns and the fabric quality was poor. I would trust Keepsake Quilting and Connecting Threads, because they seem to carry quality fabric.

I think if I would buy kits, it would help stay organized. ??????? You think maybe.

I have worked both ways. At times I love to do the shopping, others I just want to rip into a project and sew. I've purchased kits and made my own in the stash for those days. As long as I recognize the brands a shop carries I'll jump in. Just need to carefully read all cutting instructions before beginning

ditto :)

I have only bought one kit. A couple of the shown fabrics were substituted with other fabrics. Seems that they ran out of those fabrics and made substitutions. Other than that it was ok.

I must admit I have bought kits when the chosen fabric exactly my taste and I like the pattern. However I like to use kits to push my skill limit.... so if the pattern is one I've never done and it is designed for the more advanced quilter I will buy the whole kit so I can concentrate on the pattern. I find this is a good way to stretch yourself.

I did a BOM with Fatquartershop.com and I was able to complete the original 12 blocks, do another 12 blocks and have enough fabric to do another 12 blocks. That's not including all the extra fabric I got in the finishing kit for borders and such. Two quilts easy with extra fabric for stash.

My local LQS is more modest in their BOM's with the fabric and I've had to go and get more when I mess up.

Yes, be careful about the quality, if it is the fabric displayed or subsitutes, and how generous the cuts are. I have gotten burned more then once. Open the kit and check. If they do not let you run.