I have no experience with the Power2Max. Mostly because I'm invested in Quarq after a long relationship with Powertap. So Others will have more useful input on that front.
But, between the Favero Assioma's and the Garmin XC's I chose the XC's. Really it came down to 50 hours of use verses 250 hours of use on a single battery change/charge.
I chose the dual sided XC 200 model. It required a software update & a calibration to generate believable numbers. It also generates a lot of pedal dynamics (how you pedal) viewable in Garmin Connect. Whether or not that is useful to you is anybody's guess.
I know for myself, single-sided measurement is inaccurate.
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I shouldn't have to "make myself more visible;" Drivers should just stop running people over.
Car dependency is a tax.