...I took the course in warm, clear waters around Sharm el Sheikh. They want to take the course in dark, cold, murky waters in and around Belgium.
Well, good for them! if they can manage it under bad conditions than it is a plus. Do you think it would be better for practical purposes if they had chosen an easier way, as you did?
More demanding conditions mean less chance of them passing if they are not ready.
Everyone should be encouraged to take Rescue Diver course, but the certification should not be given when they are very proficient at all the skills. And if one chooses to do it under the most ideal conditions possible than he/she misunderstands the purpose of that training.
Also, # of loged dives is not an indicator. Some people simply have personalities that make them good divers fast. Those who are not prone to panic, deal with situations rationally, comfortable in water... etc.
Also, as a Northeast diver who has to deal with bad wiz, constant cold, bad weather, I feel that I am at a higher skill level than a person with a log book twice as long who has only dived in warm vacation resorts.
And I don't think you should discourage anyone from learning to dive in challenging conditions.