We bought the elementary set in pieces as it came out and honestly, I love how they incorporate higher level math alongside the basics. But it's just SO. FAR. OFF. from how I learned math that I'm trying to figure out if it truly does teach up through the higher levels of math fluently. I was a math kid and had good teachers to boot. My son loves these books, but because he's also a math kid--I could totally add Singapore on and he'd be totally fine with it. That being said, I don't really want to if it's not going to serve some purpose... kwim?
I don't know anyone that's used LoF exclusively and I'm wondering if that's because prior to this past year, the elementary series didn't exist. So people start with a lower level program and then it becomes what they're accustomed to, kwim? I know one or two that used it alongside another program, but not exclusively.
I do know that a parent on our local homeschool loop has a spouse using LoF for his college level Calculus with great success.