i weigh 145 and used to ride profile bullhorns with two different types of aluminum stems. after riding them a full year, i started getting an alarming amount of flex in the bars. if i pushed down on them they would visibly bend about 3/4 of an inch.

yoshi on the forms had a pair of 'em as well, and they snapped on him after doing the same thing.

the nashbar horns are kinda the same deal if i recall, if not cheaper quality, so its something to look out for. they'll be fine when you start out, but after enough time, aluminum bars get like that.

keep your hand position in mind as well. when you're on your brake hoods, that's a fairly good indicator of where you'll rest on your bullhorns. if it's really comfortable, you might as well stick with the same stem you've got now. nashbar brand stuff isn't something i'd consider a step up from typical stock components.