Yes, it is less likely to squish the filament (to some extent), however, while you may get higher pressure on the hobb and therefore more grip, like Hazer said, adding surface to an idler does not itself multiply grip.
I have another issue with designs like this though, and that is that you are wedging the filament between the two bearings. This pushes them out, and this can cause friction. If your bolt is too loose, the filament can actually be squished in between the bearings and break the bearing block itself, flatten your filament, or just plain jam the entire system. Under optimal conditions, it will work just fine, but under the wrong conditions it will self destruct.
I'm not saying the idea isn't sound, you are increasing the surface area on the idler, which is good, just that this may not be the best way to achieve it.
I have another issue with designs like this though, and that is that you are wedging the filament between the two bearings. This pushes them out, and this can cause friction. If your bolt is too loose, the filament can actually be squished in between the bearings and break the bearing block itself, flatten your filament, or just plain jam the entire system. Under optimal conditions, it will work just fine, but under the wrong conditions it will self destruct.
I'm not saying the idea isn't sound, you are increasing the surface area on the idler, which is good, just that this may not be the best way to achieve it.