Reading Josh’s post about power meters got me wondering if spindle power meters allow manual adjustment for known imbalance?
1. New spindle power meter & 2. Changing crank length:
My left - right power balance is routinely about 55-45 according to my assioma pedals, which makes sense because I tore my right hamstring water skiing about 15 years ago. In fact this was one motivation for me choosing pedal power meter previously so I could investigate the balance.
Now I’m looking at buying a new Crux with spindle meter, it strikes me that I’ll be cheating if I just use that power measurement.
I’m assuming I can manually adjust the calibration if I use the assiomas to compare outputs, surely this is a simple thing to do?
I’m too much of a stinge to buy another set of pedals - this was going to be a bonus in favour of buying the crux.
I haven’t tried it but the AXS app has the ability to adjust the slope of the meter so you can use that as a fudge factor.
The biggest issue occurs if your balance varies over intensity i.e. I have a lazy leg that does not push hard at lower intensities but comes online during threshold work.
From the point of view of the powermeter vendor I can understand a single sided device if your technology is in the pedal - there is a clear cost saving from shipping only one set of electronics. However if it’s in the crank it just seems to me that the spindle is a poor place to put the device. I suppose there is additional engineering and quality control for the spider based options that increases costs dramatically.
I think if you really care about the numbers you should take the crank off, sell it and buy a set of pedals.
I think your last sentence hits the important point - I don’t really care if the meter is truly accurate, so long as it’s consistent. I would prefer that it agrees better than 10% with my assiomas on my other bike, just so I can compare rides on both bikes, but I don’t care enough to pay the price of another pair of assiomas or equivalent. 
If I get the Crux, I think I’ll try running the assiomas on it for a couple of weeks, recording both PMs so I can try to get the spindle agreeing with the Assioma total power within a reasonable margin.
Never mind, the one remaining Crux available in Oz in my size is no longer available according to Spec website. boom. I snoozed and losed.
Probably academic now but I spent a very frustrating winter trying to get my turbo power to match my single sided crank power meter. (I could adjust this particular power meter to match the cranks) . I had never heard of a power imbalance let alone one that varied with intensity, cadence, fatigue or whether there was an R in the month. I was constantly altering it up and down and getting more & more confused.
I think single sided power is fine for most folks. You have a significant imbalance from a previous injury and you seem to care about properly measuring power (or at least having consistency between bikes).
It probably makes sense to invest in some flavor of dual sided solution.
Thanks to Jase, I’m now getting a Crux after all. Thank gawd that saga is over. (Please don’t jinx the delivery!)
So I will be doing some test rides with spindle and pedal power meters so I can see how much difference there is. It’s not as if I train, let alone race, so this is utterly unimportant. I’m just a nerd.