I have used both and compared the performance.
From what I have seen, the only difference is the weight, performance is identical. Both prevent bunching of the spring and both improve accuracy. In my experience, accuracy has been improved to the same degree with both guides but I will mention that some believe the full round guides to add slightly to accuracy.
Your mileage may vary, as they say. I believe its just a personal preference myself.
Maybe Hungry could arrange a range comparison at one of the clinics out East?
I could certainly arrange some range time in the Lower Mainland if people are curious.