I love my Bow Balance ones, not 100% sure they're worth the extra money but I got mine really cheap (cheaper than the "normal" ones) and I do love the wider tread on them. Not sure what difference the twist makes! I can feel the difference in them generally though and I wouldn't buy normal irons again.
If you want the "straight" ones, apparently the Thorowgood ones are cheaper and exactly the same
I love mine, I have a bodged up ankle due to popping ligaments etc during a fall then ignoring docs advice and leaping back on as soon as I was off crutches(I wasnt s'posed to ride for a few months after - oops!) So I get an awfull lot of trouble with it, and my knees..ans hip and back LOL (I'm actually only 20, how scarey is that?!) But my stirrups help relieve sooo much pressure and I can actually stand up when I get off the 'osses. I personally can't praise them enough and couldnt live without.
My sister however hates them. I never get a reason why, just simply no likey.
I love mine too, got them bought for me after I damaged the ligaments in my ankle and since I started riding again I've noticed a big difference in how my ankle feels. I'm also plagued with knee problems too and my knees are better after riding in these stirrups... can really notice the difference if you go back to riding with normal irons!