Is it normal/acceptable to ask researchers/supervisors you're familiar with (in this case, a professor who supervised me some number of years ago) about other researchers who they've likely to have met? Specifically, I'm having to decide on a researcher to supervise me on a short project, but other than a few emails, I know nothing about their personality/work-style.
I planned to send an email to my old supervisor along the lines of: "How well do you know Professor X? Would you recommend working with them?" (but with more pleasantries). Could this come across as rude, or is this sort've thing expected (in UK/US academia). Also for reference, I'm currently a PhD student in the UK and the researchers I'm asking about are all at US institutions, so I don't have any chance to meet them personally first. I also understand that this is largely dependent on how close you are with the person you ask, but some other opinions would be useful anyway.