They're two completely different chemicals.
I took 25i last weekend, and it was pretty different from LSD. Any visuals I got were subtle, such as a slight disco-effect on the walls and everything around me, breathing walls, depth-perception was...unique (it looked like everything was farther away), and of course the classic LSD thing where everything is moving in ex. such as the grain on a tree flowing, and it gave me a strange energy like being cold and excited. Trip also only lasted 6 hours, but at the end of it when I went to sleep I had some really intense dreams. Not sure if that's related or not.
But yeah, that's just my experience. I've done it again since that first time, but the next time was intentional. First time it was sold to me as LSD. Oh, and also the blotter is bitter and tongue numbing!