I also use XH-A1 as my main cam and HV30 as B-roll in weddings. HV30 is an awesome cam for the money you paid for. Also, it's a consumer cam. low light is always an issue with consumer cam. However, with some lighting, proper shooting mode (I do Tv Mode 1/30 shutter in low light), and the photo button trick to lock down gain, I get very decent output with HV30. I also color match both footage so they both look very similar too.

How is the zoom control like? Is it possible to get a dead slow zoom?

I think HV30's zoom rocker control is worst than HV20. With HV20, I can nudge it with my finger to make really slow smooth zoom. Not the case with HV30. Anyway, you can also change the zoom speed in menu.