TCP will not be able to easily take advantage of VIA features. You may eventually have to port your code to a non-Linux platform, and on other platforms, the VIA performance advantage will probably be even greater. Of course many applications won't use M-VIA directly. The M-VIA license allows modification, redistribution, and commercial use. Valid quality of service values are not specified by the VIA standard.
Reliability generally depends on hardware.
The ethernet devices supported by M-VIA should be treated as unreliable. There are several possible causes. The VIA kernel modules may not be installed correctly. The copy on receive is unavoidable for any protected communication without special hardware suport. On the receiver, data is received directly with a low-level hardware interrupt that does all the processing necessary.