I see you are a cycling coach right? Tell me why you would recommend one for MTB's? I will tell you my opinion but would like to hear yours first if you dont mind.
Thanks for answering a question with a question. That's a pretty poor dodge
I haven't stated an opinion on the matter. I am asking why you have come to the conclusion you have, since you are the one making the statement, not me.
But here are some preliminary thoughts, since you are so keen to know....
MTB is an aerobic endurance sport with some specific demands (downhill racing is different but I'm presuming we are not talking about downhill racing).
Given that good use of a power meter can be tremendously helpful in objectively assessing and tracking the performance of a rider, guiding their training workload and helping to ensure training is sufficiently specific to meet the demands of racing, irrespective of whether that is track, road, time trialling, MTB, ultra endurance etc, then I'm wondering why you've specifically nominated MTB as being a wasted application for a power meter?
Clearly in each cycling discipline there is a different balance between physiological performance ability, skill level, execution of both tactical and strategic plans as well as demand side modification (e.g. better TT aero positioning) but I don't see why this significantly diminishes the value of a power meter in MTB specifically (compared to "roadies"), hence why I am asking.
Presumably in MTB there are specific neuromuscular demands (which e.g. would be very well assessed through tools such as a quadrant analysis of the average effective pedal force and circumferential pedal velocity data from a power meter) which one can address in training to make sure these elements are covered, particularly if one doesn't have regular access to MTB venues, or venues that replicate the target events or their current neuromuscular power abilities could use some work.
There are often pacing and nutritional management strategies to consider, both of which can be very clearly assessed with the aid of a power meter. Fast starts to jockey for position, then pacing well over balance of the course are a couple of examples that come to mind.
This is aside from the typical use, that of regularly assessing fitness and how that relates to the fitness required, performing appropriate training, and of monitoring, managing and prescribing optimal training loads, and nailing your taper.
BTW - yes I am a cycling coach and no I do not sell power meters.