I have several sets of Favero Duos and a set of Favero Pro MX pedals. I've done the SPD hack on the duos so I can use SPD cleats and MTB shoes. This was before the Pro MX SPD versions were released. They all work well. Zero issues.

The Faveros are also one of the least expensive options available. And are considered as accurate as any power meters available. I simply have no reason to consider another option.

Concerning single or dual sided. I happen to have all dual sided. But I don't think it really matters, at least for training purposes. As far as I know, all power based training plans are proportional to some sort of power test, Usually a 20-minute FTP or ramp test test. As long as the same PM are used for the test as for the training, absolute accuracy doesn't matter. You could take all the values and multiply by an arbitrary scaling factor and the training plan would work exactly the same.

What I've noticed with my dual sided meters is I have a significant difference from left to right. Typically something like 55%/45%. But it's always about the same. So, if I had a single sided PM, it wouldn't matter for training purposes.

Now, if you're going to use your PM data or FTP value in pissing contests with other people, then I guess absolute accuracy matters. Or perhaps play around with data to estimate things like rolling resistance or aero drag, accuracy matters. And of course it matters if your competing on something like Zwift.

I like data, I do play around with engineering data like rolling resistance and aero drag, so it matters to me. But really for curiosity sake more than anything. And the cost difference doesn't matter to me.