With both a Tray Load Strawberry 266 and two Slot Load Graphite 400/600s side by side, it's the Tray Loader that undoubtedly has the extra structural rigidity. Fewer panel gaps, stiffer plastics and it doesn't creak whenever it's lifted or opened. I can't say that I've ever had an issue with the Tray Load drives in these machines either, and I used them as a daily so those optical drives did get quite a workout.
I've had three in total, a Grape, a Lime and the current Strawberry. They aren't bad overall.
Perhaps one of the downsides I can see is the TL's Flyback Transformer. I hear they could have a few issues as they get older.