Even if it were innacurate. As long as you're fed the same lie over and over consistently you can train to that. Now, if you have more than one PM I do see a need for it to be accurate, but if you only have 1, then you do not know any better. I could analogies with current politics but I will refrain

Thanks Ian,
My original idea was the 4iii, probably to have them install it, as they don't currently have the R8000 ultegra arm.
Pedals are nice though. They seem a little easier to upgrade too. And when you do, you have all that data from garmin that will never be used...

If your balance changes from day to day you're not being fed the same lie though (your balance may, of course, not change - it may even be 50-50 so not only is the reading the same lie, it's not even a lie!). Anyway, I think this is one of those things where people have differing opinions, possibly based on their own personal experience, and that's fine.Something that is up-gradable to dual sided in the future could seem like a good compromise (though in the 4iiii costs about $150 extra over buying dual sided in the first place). I'd definitely consider a hub further. I'm sure whatever you buy you'll love it and it will help bring your cycling on.

I will avoid making generalizations, but for me l/r balance changes constantly throughout the ride. It changes based on power, based on fatigue level, based on cadence, incline, etc. there is just no way a left-only power meter would be accurate enough minute to minute, let alone ride to ride.

Edit: I will add that those that think that taking left-side power and doubling it to get "total power" is an acceptably accurate measure of power are probably too young to remember the debacle that was the Ergomo Pro power meter. The Ergomo Pro had great promise when it was first introduced. It was a bottom bracket-based PM, which meant you could use any crank you wanted (and any wheels, pedals, etc.). Once the data was compared to an SRM or Powertap however, the Ergomo was quickly revealed to be woefully inaccurate, and quickly fell out of favor and (as far as I can tell) went out of business. I find it terribly amusing that, 8 years later, here we are again debating whether doubling single-sided power is acceptably accurate. Those of you that feel that taking left-side power and doubling it is good enough, I'll happily sell you my used Ergomo Pro.

actually srm and powertap did not kill ergomo, solid-axle cranks did

To the OP - why are you so opposed to changing out your crank?

I just got a Power2Max TypeS for $640 for my road bike, and after selling my old crank & chain rings, the power meter ended up being under $500. I've had a Power2Max on my tri bike for around 18 months with zero issues.

Just a thought.....

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because the Ultegra R8000 is sweet looking. Aesthetics aside, I agree that the Power2Max option (the Eco probably) is the best value out there.

Actually...overly sensitive installation requirements, excessive bearing drag, poor reliability, and demonstrably variable output (especially over temperature) "killed" Ergomo.

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Yeah, well... that too. ;-)

Actually, I never found it that difficult to install. The only additional requirement was to face the BB shell to ensure that the faces were perpendicular. That was a one-time thing per bike. I never had reliability issues with mine, but yeah, the bearing drag and the data variability were quite bad.

Have you looked at the Watteam Powerbeat? You can get dual-sided for under $500 and single-sided for $260. The product is fairly new (2 years) and the reviews are mixed but if you are OK with single-sided a price of $260 should be enticing enough to at least give them a try.

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I have seen them. I'm not sure about those cables sticking out but it's a killer price