I started using FIAR just recently, we've only done 2-3 books. My dd is just barely 4, but she loves to be read to and do story extender type of stuff. (I used to make up my own, but they were far more simple) For us it has really been about 3 in a row, I skip a lot of the art lessons, as my dd isn't interested in that, and some days we do more than one of the other activities. I sort of think we could almost do the stories, and then do them all again in a few years, doing the more advanced activities- but we'll see.
I do think this book was a great buy, and after we work through vol. 1, I plan to get the next one. Some of the books are classics, and I had copies that belonged to dh as a child, others I've bought used or new - here at the TP, and from Amazon. We have also taken weeks off lately when we had a lot of other things going on, so just buying 1-2 at a time as we need them seems to make the most sense, and is easiest on our budget.
At this age the only other supplimental thing I'm doing, is I have some Handwriting without tears wooden pieces and access to more of their program which we are doing. I think for children over 5 suppliments in handwriting, reading and math may be called for. There are some math activities that I think would be fine for a Kindergartner, but an older child might need more.
My child and I have both enjoyed it a lot.