I would definitely agree that the IMCR should be done with an instructor who teaches the IR.
I would also get each individual lesson signed by the instructor - just in case one wants to make use of those logbook entries at some future date towards something else, e.g. an FAA IR. I've been told recently by an FAA examiner that previous instrument training is allowable towards the FAA IR only if done with an ICAO instructor qualified to teach the IR. A lot of IMCR instructors don't have an IR. I have no idea if he's right (schools in the USA aren't bothered by this) but it's worth doing just in case.