I bought a Big Dee harness 13 years ago and am still using it. Probably not the same model as you are looking at, though, after all this time. Mine does not have a red browband. I love the bridle; it has very nice blinders and excellent leather. I'm still using the saddle and it looks great, but have upgraded to a Camptown breast collar. I did not like the Big Dee breeching; it only had one strap so I purchased another breeching a few years ago. The crupper is very nice. My horses are 30-35" and the harness has fit them all.
Big Dee has been in the business a long time. I think it would be worth a try. If there are parts you love about it, you can always change out parts you don't like over time.
I doubt anyone is using the actual complete harness he started out with! They almost always need tweaking.