I've used the terrex pros for a couple of years. I found them on craigslist for $100, which is still expensive, but since I bought them as goggles and glasses, I thought it was worth it. I don't have experience with a range of glasses or goggles, so I don't have much of a reference point. If your primary purpose for them is the occasional windy summit on a winter backpacking trip, then I think they would do well for that because %95 of the time they would just serve as an excellent pair of mountaineering sunglasses. Then when you get close to tree line you could switch them in to goggle mode. This does increase the fiddle factor though, and adds extra small items that are easy to lose track of. In full-on whiteout conditions or if you are just crushing pow at the resort, then a goggle is a way better option, but for winter backpacking, or fast and light bc skiing, I'd agree with other folks that a full coverage (in this case, convertible) pair of mountaineering glasses is the way to go.
A quick review: comfortable, good coverage, a range of swappable lenses that all have likeable/functional shades, durable. In goggle mode, they are such a close fit that it can feel a little bit awkward, like halfway between ski and swimming goggles. So for a whiteout I'd wear those, but for bc skiing (my primary use for them) I just add on the foam, but don't use the goggle strap. I get a fairly good seal this way, but I can still vent them out as needed and they are not as constrictive. Like any sunglasses or goggles, they do fog up, but I think these are a little better than others I've used. They also come with that nose piece which is cool, but my snozz might be a touch too big for it. Just thought i'd chime in since I didn't see many actual user reviews online when I bought them.
Full retail, I don't think they are worth the price, but if you can swing it, why not.
edit: Just looked at the uvex pocket goggles. the terrex would be pretty similar to those in goggle mode. If you've already got a pair of sunglasses you like, then something like that would be a good way to go, for maybe an extra oz, but less $ and less fiddle factor.