There’s a couple of things in the two-sided vs single-sided discussion. The first question is do the metrics like leg balance etc. add anything and I think except for someone recovering from injury the current consensus is that nobody knows what to do with this information, so they are not really important.
The second part of the question is what type of power meter to use, there is essentially two type of powermeters in the single sided vs double sided space. There are the true left-right balance power meters, which are either pedal or crank based (stages, 4iiii, favero, garmin). They do measure your true left and right power, the down-side is if you buy a single sided version of these only it simply doubles your power to get your full power, I come back to that later.
The second type are the spider, BB, hub-based powermeters and trainers. While some of these give you L/R balance, they are not able to actually measure it they simply look at the different parts of your stroke and calculate the balance from that, there is general agreement that the metric is even more useless than the true L/R balance, because you don’t actually know where that balance is coming from (are you simply puling more with one leg or do you actually push more with the other leg).
Regarding a question what type of powermeter to get. The issue with estimating power from a single sided measurement is that you don’t know your actual balance and importantly your balance might change significantly with effort. Thus your reported power might be quite different at different effort levels to your true power levels, which can make intervals estimated based on e.g. FTP either harder or easier than they should be (somewhat less of a problem with xert).
A similar argument applies to the shimano dual-sided powermeters, which report wrong numbers based on pedal style (i.e. effort level), GPLama has talked about that quite a lot (watch his videos if you are interested).
What I would do is either go for a spider (quarq, rotor), or dual-sided pedal based or non-shimano crank based powermeter. I don’t think the small savings of a single sided version crank or pedal based powermeter (e.g. Assioma 450 euro vs 700 euro) is worth the inaccuracies. However, I would not care if you get true (pedal/crank-based) or estimated (spider/BB based) L/R measurements, go for the best deal you can get.