Open fronts and Splint Boots/Brushing boots are fine for stadium jumping - because you are in a nicely conditioned environment with nice deep sand that is grommed and even.
So when you are doing stadium - there's your answer :)
CC - one should want more protection for their horses joints because the grond is harder, the terrain is uneven and our horses take much more doing that, than they would stadium.
I'm not saying SMBs are the be all and end all, they are all I know though because I've used them for such a long time and they've done their job as they were created to do.
BUT what one should look for in a good, protective sport boot while doing CC is something that ABSORBS THE SHOCK our horses joints take - and brushing boots/splint boots do not do this.
Now, Woof makes great Eventing Boots. They are lined with Neoprene, which is what abosorbs the shock, while protecting and allowing air flow. Woof Cross Country Boots - Dover Saddlery.
Eskradon makes boots that are meant for Eventing as well: http://www.doversaddlery.com/product...&ids=419334081
Same with these neat one's: Tri-Zone Cross Country Front Horse Boots - Dover Saddlery.
Those are the type of boots made specifically for eventing - to meet the needs of our horses joints.
I wouldn't put basic woof's on my horses legs for eventing - they don't abosorb the shock.
I like the looks of those Tri Zone boots.