I'm considering getting a dual-sided 4iiii power meter for a Shimano 105 5800 50/34 and have it installed by my LBS. Does anyone have any experience with this particular powermeter? How do you or did you like it.

No experience with their dual-sided power meter. BUT I do have a a left sided 4iiii crank arm PM and I like it. No complaints. Price was right. And a Canadian company to boot! Cheers.

I am using an Powertap unit now, but they were purchased by SRAM/Quarq so I can't support them any longer. Mine is almost shot so I am going to 4iii next. Unless somebody does a pedal based that works with shimano cleats.

Dual sided crank based power meters with Shimano cranks are notoriously inaccurate because of the asymmetric design of the spider and chainrings. Probably better off going with a singled sided setup or a spider based unit like the Power2Max NGeco.

Here is one article where Shane details the issues. There are others if you want to research it.

https://gplama.com/2019/06/29/shiman...-power-meters/

Looked long and hard at the 4iiii Shimano Crank PM
Went with the Stages just because of the temperature compensation.
FYI most all of the Hollowtech II cranks are mix and match.
I was running 6800 cranks, but purchased the R-8000 left side and installed it on the 6800 right side I had.
No issues. Nobody even noticed the color difference.
Save my pennies and finally went R8000 right side for dual.

Barry

Have you looked at the Favero Assioma power pedals? I have the Duo version, and have been happy with it. Competitively priced and accurate enough for my purposes.

Very interesting. Actually the most interesting bit of info I've learned. If I decide to actually get the power meter the Favero Assioma seems appealing with one exception. I want to be able to ride in mountain bike shoes like my current Sidi Dominator Mega with SPD cleats as I sometimes have to do extensive walking on some bike rides.

There is actually a video out there of a guy that hacks the Assioma’s to work with spd’s

I have the Assioma pedals but would not use them offroad on a mountain bike for fear of rock strikes and crashes. For offroad get a spider based power meter such as Power2Max. I had Assiomas on my gravel bike and just replaced them with a Power2Max.

My P1 Pedals recently took a powder - bearings are rather worn and the left side started dropping out. Considering they only lasted for about 3 years and require a $300 service to bring them back to life, I decided to switch to a crank/spindle based PM instead. I really wanted another true dual sided PM since I suffered a very severe leg injury years ago and the dual sided PM helps me focus on my injured leg. I looked in to several different power meters including the 4iiii but, decided on the Rotor 2inPower crankset with direct mount chainrings and I couldn't be happier. It's a versatile unit that comes with multiple BB adapters so I can move it between bikes if I want and it also has built in temperature compensation so I don't have to calibrated it every ride.
Just another option to consider....