I have my Ride-Rites connected with a "T" and only need one Schrader valve to keep them perfectly equalized. I've experienced no problems whatsoever in handling. The theory about the air moving from one bag to the other is simply the weight shifting during turns. It is no worse than without the bags.
I think the advice about not tying them together with a "T" applies to trucks which are unusually topheavy, such as pickups with campers in the bed. In such cases, separating the air bags can help when cornering or in evasive maneuvers by preventing the air moving from one side to the other. However, a problem arises if the air bags are not kept equalized all the time, so a leak in one side can cause an unbalanced side-to-side situation and create undesired difficulties.
As usually, there are pros and cons for each case.