The R91 has been a clinic staple for a long time simply for ease of use and price. I’d advise turning up for your treatment having shaved using whatever you plan to continue using for your daily routine. If you used an R91 that day and that’s longer then you plan to shave to then potentially your black hair will appear darker and they will match to that.
If in any doubt then ring the clinic and speak to Simon or Paul. Of course I’m sure the R91 is okay as these boys know what they’re doing but if you don’t plan for the R91 to be you chosen shaving method then for me it makes the most sense to arrive at your appointment having used that method.
The only benefit of using the R91 is that it may allow the practitioner to see more clearly your remaining hair and where to concentrate their attention.