Looking at their site, it would reveal a typical Ha filter bandpass. First image is the 6nm and the second the 13nm. All appear to be around the 656nm. I wouldn't be concerned about it the "blue" shift. These graphs are misleading as there is a grey line that hovers over the visual spectrum. I originally thought that they were trying to explain that was what the ha filter bandpass was
The third image is the Custom Scientific 10nm 50mm Ha filter I use at present. They personally test each filter and provide you with a reading output result. Nice.