Thx Hamish for some confirm on this.
Asked Lemond themselves and got this:
I would definitely not suggest operating the Revolution without the fan shroud installed being that it could cause injury to one’s self. And yes, It would throw off the power curve of the fan and cause inaccurate readings. You could definitely still pull a wattage reading off a crank or pedal based wattage meter, but I definitely do not suggest operating the Revolution without the shroud, and it seems to me like the advantages gained are not worth the risk.
Well, as long as one is on the bike and don't have any kids or pets nearby, I suppose it's still a viable solution if the only way to use it in one's flat is if it's quieter. The powercurve he mentions, is from the Power Pilot Meter(PPM) one can buy to the Lemond as an addition.
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