The rubber torsion suspensions usually ride real good as individual axles. The pluses are that they are independant and the manufacturer can use the steel tube as part of the actual trailer structure so that they are easier to install.
The down side is that the rubber usually lasts 20-25 years and sometime after that timeframe, they start riding rough because the rubber is getting hard. The rubber, in most cases, is not easily replacable, so you need to replace the axle. They don't have an equalizer on tandem axle setups like the leaf springs so that each axle may have to take more of a load than what they are rated for.
Example: If the suspension travel is 5" and you are going over a 7" speed hump, your 8,000# trailer will have all 8,000# (minus the tongue weight) on one axle that may only be rated for 4,000#. Some of the rubber torsion manufacturers recommend rating each individual axle at 1.25 times what the load is intended to be. So your 8,000# trailer should actually use two 5,000# axles.
Some manufacturers don't recommend them for triple axles because the tremendous side load can pull the torsion arm out of the axle tube.
They are a good axle setup and if I found the "right" trailer with them, I wouldn't turn down the trailer because it has a rubber torsion suspension. I prefer the leaf springs with the equalizer on multiple axle trailers. The nicest is the leaf spring split in the center for an independant suspension. These were made by Dexter and are rarely used because it is more expensive and there needs to be a center member on the trailer frame to attach the center pivot point.
Ford F-350 4x4 Diesel
1988 Avion Triple Axle Trailer
1969 Avion C-11 Camper