Do You need one?

[Flyflicker]

If your tow vehicle has a 9000# tow weight, do you need a Weight distributing hitch for a 3500# trailer?

[m.hony]

You may not. You probably only have 350# tongue weight.
Does the tow vehicle squat in the back when the trailer is hitched?

[Lumatic]

A WD hitch also provides additional attachment points in addition to the ball and safety chains which is a safety factor, Depending on the hitch it also adds sway control.

[dkottum]

Probably, but there's more to setting up a well performing truck/trailer combination than those numbers. Best not to approach it with "What can I get by with". Better to look for a good combination of truck/hitch/trailer.

[m.hony]

Some weight distributing hitches provide additional attachment points. The Equal-i-zer doesn't.
If the trailer were to be separated from the tow vehicle, the weight bars would just slide right out of the saddles.
We never use weight distributing hitches on 7,000# GVW car trailers, cargo trailers, and utility trailers, but we do use weight distributing hitches on 14,000# cargo trailers.
It is about front axle weight. On car trailers, you can move the car forward or back to get the balance right. On cargo trailers you can load it with the weight from the front to the axles. With 1,000# or more tongue weight the rear of the tow vehicle squats down and the front is in the air- less steering control and headlights blinding other drivers. The idea is to transfer weight to the front axle and trailer axles leveling the entire combination and bringing back steering and braking control and safety.
With 350# tongue weight these situations will never come into play.

[MrUKToad]

Properly set up, a weight distribution system can only improve your towing experience regardless of the TV/Trailer combination. Add some sway control or elimination as cheap insurance and you're all set to go.

[m.hony]

A 3,500# GVW trailer is like a 4-wheeler or golf cart trailer- single axle, 2 tires.
I have never used a weight distributing hitch or sway control on a trailer that small and never had any trouble.
No strain on the tow vehicle's suspension. No tongue weight to speak of. A small 4 cylinder tow vehicle will do it.
Your 9,000# towing capacity indicates the tow vehicle should handle a 900# tongue weight. Your trailer should have a 350# tongue weight or 1/3 of what the vehicle is capable of. There probably is no rear squat and no misalignment of the headlights and no loss of steering control or braking with a trailer that light.
I would think sway control could be an issue, at least more important or higher priority with a trailer that small.
Sway control will buy you more peace of mind than weight distribution with a rig that small.