The one time I used a store-bought divider, it felt very flimsy and was nearly clear, my boys could see each other a little too well for my, or their, liking, plus the little holes were so small water movement and heat seemed not to travel properly. Plus, there was this huge black line at least an inch in width in the middle of my tank that I really didn't like the look of. That was a couple years ago, I dunno if they make them differently now, but I really didn't like my store-bought divider at all, I even had some trouble with getting it in straight and it bent quite a bit, though that could have been me.
Now, I make all of my dividers....they're cheaper and just feel more stable to me, and you can double up on the mesh to help limit your boys view of one another. I've never really had trouble with them bending too noticeably...I'm not sure if its because I double up(which seems to make them more stable/straighter as well)or I'm rather meticulous about measuring and cutting the mesh, but I don't really see much of a bend when I look in my tanks. The little binder-end things are nice and small, and even though I double up I've never had trouble with heat distribution or anything.
So I'd say homemade all the way....but thats just my experience/opinion xD If you feel like a store-bought divider would be better/more convenient for your tank then go for it.