OzarkGrey....Great question, allow me to share my expieriences with you. First of all, for liability reasons trailer manufacturers will not produce a trailer that is unsafe and/or untested.
I have bought ,sold, traded and used many makes (Titan, Diamond D, Coose, Trailman, Travelong,WW, Travelute,CM, Stidham and Featherlite among others) of single axle stock trailers here in South Dakota with both torsion and slipper type suspensions.
The smallest being a 10' on a 6K axle with 235/85R16 10PR, and the largest being a 16' on a 8K torsion axle with Michelin XTA 215/75 R17.5 18PR BSW tires.
These trailers ALL pulled easier, turned with less bind under heavy loads on hard surfaces, and defineatly no problems when having a blow out. The trailer stayed true did not whip or sway under both loaded and empty conditions and the corner did not drop.
A problem with those cute lil ole 3500# or 5200# tandem set ups on 15" rubber is when making sharp turns under loaded conditions on any hard surface will result in one maybe two bent axles.
Also replacing 4 "avgerage" 15" tires that are common on most goosenecks of this size is more expensive than replacing 2 well made 16' 14PR tires.
Changing tires under loaded conditions, say a load of 500lb calves along the interstate can be problematic if you don't have the right equipment, mainly the jack,(either a handyman or a 20ton bottle jack). Other than that my expieriences with single axle livestock goosenecks have been very positive. And I would recommend one to anybody considering a purchase. You can get by with a 1/2 ton pick up pulling the 10' and 12" goosenecks. But on a 14'-16' gooseneck stock trailer I would recommend a minimum of a 3/4 ton pick up.
As of this writing I have in our shop a used 14' S&H gooseneck that we cut the lil cute 3500# axles off of and are replacing them with a single 7000# dexter torsion axle and michlin xp rib radials 235/85R16 tires on 8 hole modular wheels, along with new wiring, a rumber floor, and replacing the slat sides with solid sides which is easier to enclose in these tough SD winters, and new paint, this trailer has been sold before completion.
While some concerns were identified in some earlier posts, my expierience tells me that most of these concerns are with out merit.
I hope my 2 cents helps you make an informed decision!!