There are some people who never need IF#1, even with the IF#2. I am one of them. I've only taken 4-5 IF#1 capsules in all these years (and that was when I ate meat/cheese after not eating any for weeks/months, and constipated myself).
Some people can achieve more bowel activity simply by taking a fiber product. Heck, Metamucil helps a LOT of constipated folks.
But you ARE correct - IF#2 does have the bentonite, and that can be even MORE constipating for people that are already having trouble achieving natural bowel activity.