A double layer gives you a place to put the pad. Throwing the pad in a single layer works, but I can tell you from experience that if you use a quilt and don't have something between your base layer and the pad, you'll stick to ccf. Pads also have a habit of shifting on you, or in the case of a thermarest a little too well inflated, squirt out from under you; the pad pocket defeats this tendency. In a tent, I was the one rolling off the pad; in a hammock, I didn't have a lot of trouble with a ccf even in the Hennessy, other than my long johns sticking to it. I could have fixed that with a sleeve made of ripstop over the pad, but chose the Blackbird for additional reasons.

A Blackbird has a footbox to make it easier to put yourself on the diagonal. Most gathered end hammocks have a "ridge" that can be dealt with by laying on the diagonal, and the wider the hammock/the more sag you use, the easier this is.

The Blackbird has tie outs, a shelf, a lot of room (least claustrophobic I've encountered), a fixed ridgeline (sets the sag of the hammock regardless of the distance between trees), and a full bugnet with a full length zipper that's integrated in such a way that it doesn't impact the lay of the hammock whether you actually zip up at night or throw the netting back. (Last six overnights I haven't bothered to zip up.) The rings/straps of the Blackbird (on the strap option) are easier to fiddle with to raise/lower or center the hammock - but any hammock can be updated to rings or a ring buckle on the suspension with little effort.

Speer type hammocks are fairly simple and lack a lot of the features possible with the Blackbird. Brandon also customizes the Blackbird - puts the footbox on the other side if you want, or uses heavier or lighter material you provide, etc.

I can tell you that if you order a Blackbird and don't like it, you can make a little money - they disappear off ebay for more than you pay new. Some people don't like the waiting list. I watched one sell at hammockforums.net within an hour of posting - bam, gone.

This is not to sell you on the hammock - I just have no experience with a Speer. Lots of people like the Speer just fine. I just have no reason to get one now that I have a Blackbird, no weight savings there to be had, nor does it have some of the other features I've grown accustomed to having. If I were to recommend to someone who has no inclination to tweak or geek on the hammock, it would be a Blackbird every time, simply because it's so straightforward, no knots to tie, good workmanship, and the strap option has worked so well with our huge California pines, firs and cedars.