Left leg only.

Left leg only or not - if its the right price interested :-)

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He who understands the WHY, will understand the HOW.

It doesn't get installed into the bottom bracket. There's no hollow portion there. Rather, it gets installed into the hollow portion of the crank spindle.

The one sided Rotor powermeters use the same configuration. DC Rainmaker has also presented info on the same type of powermeter under development for Ashton Instruments. Lots of PM options being developed. These spindle based meters will be most beneficial for mtbs, fatbikes, etc that don't use typical cranks, chain rings and bottom brackets. The price may be low enough that swapping the, around isn't as big of a concern as it has been with pricier pms.