I know I definitely don't belong in the 4 boards, but I have a 1.5" CHI Turbo and I love it! One of my very best friends has 4a/b hair, and she comes over to use it all of the time, she says its the best straightener she's ever used on her hair, and it definitely gets her hair pin straight.
She's un-relaxed, but wears her hair straightened most of the time. Is that considered natural?? I'm a wimpy 2c/3a, so I have no clue.