I had a 32’ span, used two per truss. Plus blocks at the headers
Since I posted my contempt for the prices, these have come down in prices below 3 dollars. I'm a Home Depot fan, so I didn't mind calling them out on their over pricing. The price now, 8-22-2018 is in line with what the product should cost. 2-3$ is reasonable.
Once in place, they don't need to be removed. It's ridiculous to think they can or need to be removed. They space the trusses and that's all. Once the trusses are in place, you need to support them with 2 x 4's tied to the main floor to keep them from folding like a house of cards. Talk to local builders/framers for the same information. These are spacers and not meant to support an the entire trusses for very long.
Given the comment below, I will assume that the suggest price was in the range of $15+.00...which was clearly a typo. Typically speaking, they range at around $2-$3 each, give, or take. As of today, Feb '18, it's $2.85 ea.