Vic, Regardless of the hitch type (and I definitely agree that a load equalizing hitch is the only way to go), are you sure your Explorer will have the muscle to pull a 26' Hi-Lo?
Your original question regarding the need for sway control depends on several factors like: trailer balance and how its loaded, tire type, condition and inflation, etc. Its really difficult to predict if an unfamiliar trailer will fishtail after being personalized. For example: Unloaded, our 19 footer tends to fishtail in certain conditions. Fill the water tank, located in the forward right corner, and it NEVER fishtails. Our 27' Towlight, has yet to show any fishtailing tendencies, empty or loaded. Go figure!
Suggest you talk to the previous owner to see if they had a need for sway control, if thats not possible, you may want to go with the anti-sway option for peace of mind and just to cover yourself under all conditions/situations.