According to
this review, the difference between powerPod and a Direct Force Power Meter is less than 2% on average, on rough roads (where powerPod is less accurate because estimating rolling friction becomes delicate).
So, 2% difference would be an upper bound, and it is not entirely clear that the reference DFPM is absolutely correct. If you look at other reviews, you'll see that the charts show several PM tracking closely but with some differences (measurement error).
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I personally would not spend close to a thousand dollars for a power meter. I was lucky to get a used Stages (left crank only) for $200, and am happy with it. Otherwise, I would have seriously considered the PowerPod.
Note that the powerPod is a computer without display. It will record data, meaning that you do not have to ride with a computer (Garmin or other). The downside is that the battery is said to last 20h, so you'll have to recharge every few rides. (Stages runs on 2032 batteries and lasts something like 200hrs. I ride with a Bontrager Node 1.1 with battery life measured in months).
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Final note: DFPMs, contrary to what the name implies, do not directly measure the rider's power. They measure the amount of tiny deflection in sensors. This deflection is used to infer how much pressure is applied on the metered instrument (pedal, crank, wheel, hub and such) and this amount of pressure is used to estimate the amount of watts produced by the rider. This is not trivial. For instance, in another review DC Rainmaker notes that most DFPM (at the time) lose accuracy with elevation changes (because elevation impacts temperature and pressure).