please remember that I am only a first year beekeeper and nowhere near as experienced as others who have contributed here.
I am not familiar with your local climatic conditions- I come from Adelaide Australia and our weather is described as ‘Mediterranean’ it certainly isn’t subtropical. Also we do not have the same issues that face beekeepers in other countries or even other parts of Australia: we have no veroa, I have seen no SHB, and we don’t have CCD.
However I think in some ways and some areas the California weather is similar to ours?
Currently between my brother, mother and I - we have 5 hives running flow frames. None of them has a second brood box and none has more than 10 frames of brood (most of them are 8 frame hives). To date (touch wood) we have had great success- harvesting may kilos of honey over the season this year. All colonies seem well.
One of my hives has had a (hybrid) flow super on it for three months- and the bees have yet to fill a single cell frame. However it is the odd one out- every other hive the bees have taken to the flow frames at different speeds.
We never added a super until the brood boxes were quite full- every comb fully drawn- lots of bees, etc. .
As far as bees ignoring flow frames- it seems to me like this mostly occurs when they are not yet ready to store large amounts of excess honey for whatever reason. If the bees are ready- they do not have issues taking to flow frames (in my experience). By way of example I had one very strong swarm caught hive: when I placed the flow frames on it I was amazed to see that they had filled out all the cracks with wax within 24 hours- and were laying in nectar within a few days. 6 weeks later the super is nearly full. Another swarm took over two months before they did much work on the frames at all- then they abruptly started and had entirely filled them within a few weeks. I harvested and they filled them again within a few weeks.
If it is really true that in your area no one ever runs hives with a single brood box successfully- then perhaps what I am saying is not relevant to you.
However- if I was you- I would be tempted to see if I can run a hive with just a single brood. From reading on this forum it seems like there are quite a few cases where people try to build up two full brood boxes- then add the flow- only to see that the season comes to an end before the bees can do anything much at all in the flow box. If your plan is to remove the flow super overwinter- then you would have to harvest whatever unripe nectar was in it- and hope for better luck next year.
If I was you- and I had more than one flow colony- I think I would be tempted to see if I could get away with running a single brood box as a test for at least one colony.
whilst it is true the bees should always come first- if that means that they can never fill a single flow super over a season just once- then you may as well run a top bar hive or whatever and forget all about flow hives… I want my colonies to thrive and survive- but if I am honest the reason I have a flow super is I also want to be able to harvest excess honey! the two should not be mutually incompatible.
Still as I said- I am not the expert and I do not know what your conditions are.
good luck with whatever you decide.