If you want a number that is accurately transferable to events and categories riding with OTHER people then duo is the one to go for. UNO opens up a large margin error here with say leg imbalance of 10% and 2% accuracy +/-.
If you only need for training then power data is just a numbers game and data only need to be relative to a single source as long it’s a consistent source. So an UNO is more than adequate as long as you are committed to using it forever. The minute you decide to bring a dual sided power meter in to the equation all of your training numbers need to be reassessed
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