OK... this is the second time I've seen this here. (this spring) AND... I don't normally like to stir the pot... but you guys are a bunch of worriers.
A heavy single axle trailer, with brakes, is good for 3500 Lbs. The empty trailer probably only weighs 900 lbs. That means you have 2600 lbs available to put onto the trailer. PERIOD !!!!!!!!
Death wobble isn't from an overload. It's from being tail heavy. (that condition is painfully obvious in the vid above) AND... if you have functioning trailer brakes... all you need to do is reach down, and touch the controller. It will straighten you out. AND... a duel axle WILL NOT stop death wobble !!!!!!!!!!!!!!! When I was younger (and dumber) we had a loaded 3 axle trailer got a wobble because is was loaded wrong, and we were trying to tow it with a Jeep Cherokee chief. We luckily got it under control, pulled over, and move the toys around. (a sand rail, dune bugy, fire wood, a couple dirt bikes, and Honda Odyssey)
A duel axle doesn't make things necessarily safer. It's not like you can drive around with a flat. Because of the rocker in the springs... you will still be dragging a rim/wheel if you have a catastrophic tire fail. If you want to add a real layer of safety... you need a "Dully" set up. (and they don't' do that with little trailers)
And finally... it's a pain in the butt to move a duel axle trailer. Especially if you need to put it in a tight spot. I can move a single axle by hand in my driveway. It pivots and rolls easy. Heck... even my loaded double jet ski trailer will move by hand. But you add that extra axle, and it won't pivot. SO, you have no choice but to get out something to move it with.
SO... to the OP... if that weight capacity is enough for your tractor and implements... and you don't need a bigger trailer for anything else... then save the $$$, and aggravations of a duel axle. But keep in mind, it may have a 3500 lb axle... but without brakes... it's only rated to 2990. So, do the math with the actual numbers, and make a decision. (and put a spare tire on whatever you buy)
That's my story, and I'm sticking to it !
****EDIT***
to answer your question... yes... I pull my BX with FEL on a trailer like your bottom picture.