5 volumes in 5 days sounds pretty doable if you read it like you read English (whether you understand everything or not doesn’t matter, as long as you understand what you do, and don’t stop for what you don’t).
I personally think it’s the easiest we’ve tackled (I found Yotsuba&! quite hard when I was starting out and found this for myself instead, but I acknowledge that many people think Yotsuba&! is super duper for beginners).
I can’t speak for some of the earlier reads, and I’ve only read volumes 1 & 5, but Flying Witch is easier for me. I gave up on Yotsuba and found FW far easier than I’m finding Fruits Basket (TBH, I’m struggling with it and considering giving up because I’d rather have more fun in my reading time). Laid back Camp was more difficult for my level in terms of no furigana and lots of camping vocab, but I think I was probably more invested because I loved the anime so much.
I’ve been an avid reader all my life and look forward to the day when I can consume native media at your kind of speed. One of the things I love most about book clubs is having all of the gold circle crew along to inspire us to greater heights.