I count myself a lucky one. I sent 12 medium to large boxes from Springfield, MA to Phoenix, AZ. I expected it to take 2-3 weeks. They arrived in one week! All boxes were there. Only one of them was mangled, but I take responsibility for not taping it well enough.
There is no guarantee with Greyhound Package Express. It's a cheap service with generally low customer service. But if you want to take the risk, I say go for it.
There wasn't anyone at the Package Express desk when I arrived. I waited for about 5 minutes then asked the security guy where the attendant was. He was quite rude. I ended up leaving and returning a few hours later. The ticket attendant went to grab the package express attendant. He was very helpful. I wish I remembered his name. But he was gracious enough to put the boxes in my truck for me on both the trips I had to make.
Will I use the service again? Depends on the circumstances, but I'm not ruling it out.