I'm looking at getting a Burley Flatbed and I'm considering getting a used one. I see there have been some changes over the years, especially where the trailer hitches to the bike. The early ones (circa 2005), seem to have a much larger plastic assembly that attaches to the rear triangle. The later ones seem to have a much smaller fitting that gets clamped in via the quick-release axle. I think there may be some other minor variations, but just trying to keep it simple for now.

Thoughts on the differences and which is "better"?