I'm not aware of any risks.

There are definitely benefits to vaccine diversity. The Oxford ChAdOx1 virus involves putting a modified chimp adenovirus into people. People don't have immunity to chimp adenovirus, so it infects them and delivers the spike protein, which elicits immunity. But that might also elicit immunity to the chimp adenovirus! If that happens, then a later does of the vaccine - say, for a new strain of SARS-CoV-2 in a year or two - might not be as effective, because immunity to the chimp adenovirus will stop the vaccine delivering the spike. In that case, having a different way to deliver a vaccine will be a life-saver.