After reading your post last night, Ken, I went to the mail box and there they were. Thanks very much, Gretchen. So I took one to my chiminea, popped a micro-brew, and did a burn of a full disk. There was no breeze at all, and ambient was 47* F. The actual weight is a bit lower than 4.0 oz. Mine averaged 3.73 oz. The disk was easily lit with a Bic, and the flames spread quickly over the entire disk. Here's a photo of the disk getting uniformly warmed up:

After about 4-5 minutes we had a full bloom of the flame, which was about 9-10" above the top of the disk. Pretty impressive, I thought.
The flame continued at a respectable height for 27 minutes, when it began to die down. At 30 minutes, there was still a bit of flame, enough to be able to add some kindling and get a real fire started. Gretchen was kind to provide me with some extra disks, and if I have 4 extras after I've done some other tests, I would like to place 3 of them in a close triangle, and place a 4th on top. It would be fun to see what that does, as far as fire size and length of burn.
OK, so this morning I compared the fire starting abilities of a pj/cotton/wax paper, a 1" piece of my preferred Strike-a-Fire sticks, and an equivalent weight of some Relax-a-Fire "dust" wrapped with wax paper. All samples were 4.5 grams, for an accurate comparison. There was a barely-perceptible breeze, and ambient was 50* F.
Front left: Relax-a-Fire
Right: Strike-a-Fire
Back: PJC
The Strike-a-Fire was the easiest to light with a Bic, while the other two took an extra effort to get the wax paper to burn.

The Strike-a-fire had the most robust flame, which lasted 5 minutes. Its flame-out was at 7:30 minutes.
The PJC was reasonably robust (once it got going) for a full 9 minutes, with flame-out at 11:30 minutes.
The Relax-a-Fire never really produced a robust flame compared with the other two, but it was OK for 5 minutes. Its flame-out was at 7:30 minutes.
So it appears that the petroleum jelly/cotton is the clear winner as far as length of burn time. I will probably continue to use the Strike-a-Fire, due to the convenience of carry (no mess, ever), and also because I don't need the extra burn time to get my fires going. The Relax-a-Fire dust wasn't very impressive, but I will try it again with a carefully cut 4.5 gram block of it and see how that works. (Edit: a few days later I cut a small 4.5 gm. piece from a bigger block, wrapped it in wax paper to keep everything contained, and I lit it up. The size of the flame, the time it lasted, and the flame out was identical to that of the dust).
My next test will be to see if a 25 gram block of the Relax-a-Fire will boil 2 cups of tap water. If it does, I will then see what a 17 gram block will do. That's the weight of both alcohol (.75 fl. oz. of SLX) and also Ready Fuel gel that it takes me to boil 2 cups.
Then there's the business of seeing if 4.5 grams of Light My Fire Maya Dust will compete with these as a fire starter. I've never actually tried that.
More to come…