I wouldn't expect Deliverr to add much, if any, environmental impact.

The way they work is by partnering with hundreds/thousands of warehouses throughout the US. The merchant sends units in to a few of these, and now the units are closer to the end customer, so it can get there faster.

Whether it's all stored in one central warehouse, and then distributed, or done via Deliverr (& Amazon FBA & Walmart's) way, it still needs to get from A to B. Just now it's closer. There might be a little extra shuffling.

What I love about Deliverr is they have very predictable pricing. I used them for some small units I experimented with adding to my catalog.