Peace: Here's the problem I had with a curved track on my Catalina30. First of all the travelr car was of poor quality. The 4 rollers were cheap plastic and over time they deteriorated causing a great amount of friction to be generated.
At the Catalina30 national events they generally stick the Catalina national team with the crappiest boats they can find (except in So Ca where I knew who had the good boats we could borrow) and those boats had the curved track. Since I was the mainsheet trimmer those tracks caused a problem for me. Sometimes, actually most times, under heavy load I had to put my foot on the bulkhead to move the traveler.
Here is the major problem with the curved track traveler. When I'm trying ONLY change the ANGLE OF ATTACK and not touch the mainsheet because I don't want to change the set of the sail the action of the travelr car is what causes the problem. Say I want to ease the traveler down. The car in now going downhill and the force excerted by the mainsheet is pulling on one end of the car causing the car to lift up and the force goes to the front ball bearings.
I could not wait to convert to the Garhauer straight track traveler. It has a million ball bearing that are machined 2 or 3 times and the car is virtually friction free. Without any load on the car you can flick it from one side to the other with a snap of your wrist.
The curved track traveler was probably designed to look trick but the designer probably never used one.
My vote is for a flat track traveler.