I bought (well, won actually) a pair of 10ft roping reins and I loooove them. I like my split reins too but I had them mainly for the added length. Now that I have some nice long roping reins, I'm addicted. I love being able to hop off in the middle of the trail, loop the reins on the saddle horn, and do whatever I need to without worrying about a rein dropping, or never having to worry about dropping a rein mid-ride and having to figure out how to pick it up without stopping (however, that makes for some great tests of balance... haha). I've found that 10ft is enough to be able to really give my mare her head when she needs it and still be able to have a small loop beyond my hand (I dislike having to hold the very edge of the rein to give her her head and praying that she doesn't trip and cause me to lose the reins completely).
If you're interested in long roping reins (I hate the look of tied together split reins, it reminds me of camp where all our horse tack is cheap junk), I got mine from Sunset Halters ( Roping Reins by Sunset Halters
). They're really comfortable in my hands, and they're mildly weighted so they're extra great for neck reining.
To answer your question about why people dislike connected reins so much: I think it's the whole getting a leg through thing. It's happened before at my camp (we tie all the split reins together, usually in the spot where the kid should hold on, because the kids that ride the horses have a hard time keeping track of 2 reins at once) where a horse has gotten it's foot through the loop of reins and since the reins are only around 6/7ft, they freak out since they feel confined. I think if longer roping reins were commonly available people would have less of an issue, or if people took the time to loop those reins over the horn so they can't fall down the horse's neck. Now we use rubber bands to connect the reins at my camp, that way the horse can easily break the rubber band with a little struggle instead of terrifying itself because it has a rein tightly holding it's leg.
I think split reins are harder to step on that a connected rein (since they end up dragging off to the outside of the legs, usually, unlike a roping rein that hangs down directly under the jaw) and that's why people are less worried about them, or maybe people don't leave horses tied/loose with split reins because they see that that's a bad idea... I'm not entirely sure.