Cliff,
Don't mean to sound negative but I can't think of any good reason to use these axles over a standard torsion axle for a conventional teardrop. If you were building a wide trailer and wanted to have a dropped floor between the axles then they might be worth looking at. They have a fairly large mounting footprint, which is good in some ways.
In order to use half-axles like this you'd have to have some structure to pick up the inboard mounts. That would almost surely weigh more than a standard single-beam torsion axle, then you'd have to keep an eye on the alignment, both toe and camber. I don't know if they built camber into the mounts so that you could mount them to a "flat" bottom structure of your frame.
With these axles you have two things that are fixed. The weight rating is for 2000# per pair. That may be a little stiff for a conventional teardrop, it seems like many folks will use an axle in the 1500# range. This depends on how heavy a trailer you will be building. For a torsion axle the best ride will be obtained with the axle rated for the max weight to be placed on it. That weight is in a fairly narrow range with a teardrop trailer, unlike a cargo trailer that is carrying who knows what load at any given time. The second item is that these appear to have about a 20 degree down start angle, which is good in most cases for best ride...it's just not something that can either be adjusted to suit your needs or custom specified as when you order a new axle from a dealer.
Who makes these axles? You can call Paul at R&P Carriages and he would probably fill you in, I've talked with him several times when ordering parts and he has usually been available, very nice folks to deal with. They may be made by a name brand outfit....but maybe not.
If you were to shop around you could probably get your hands on a new custom spec Dexter Torflex axle for the same or less money that would meet your needs. Maybe I don't understand what you are trying to do, but it would seem that you need to settle on a trailer width first, then get an axle that meets your needs and is simpler to work with. See this recent thread for some price discussions.
http://www.tnttt.com/viewtopic.php?t=34779&highlight=axle+price
Bruce