I actually find Regal very responsive to emails. I've never had an email take longer than a day to be responded to and most of the time, it was done within a few hours. In my experience, they're no different than any other MSC in terms of email response.
I have found problems with the instructions. I find they're a bit vague in exactly what they want. The written examples are somewhat helpful, but the editor for the past while, Wendy, can be a bit difficult. She'll dock a point off here and there for things that are nonsensical and she'll miss whole parts of your narratives and then send them back for clarification when what she wanted was already clearly written. Her grading system seems completely arbitrary.
I've never had a late payment with this MSC and they've always paid within their 90-day turnaround time, but I have noticed that checks are dated weeks before they're sent out. I wouldn't suggest taking a Regal shop unless you have the cash to pay off the bill yourself. Interest on these shops will kill you if you don't have that kind of free cash to let sit.
Generally speaking, I don't take a Regal shop unless I've got a specific reason to be in that particular place and it's going to save me money by taking the gig. I don't see that changing in the future, but I certainly wouldn't do it for the money. It's not worth the hassle.