I don't think using mid-drives on the flat is a problem. It's the other way around. If you have serious hills, a hub drive will strain because it can't be geared to keep it turning fast enough to be efficient.
You buy a hub drive because it is easy to set up. The motor turns and if you want to pedal, you pedal. The two drive systems are mostly separate. There's no complexity. People say they are not as efficient, but it's not proven anywhere with any precision. I have a 20 pound Magic Pie and it is very efficient and it will climb most hills efficiently. But that's a heavy motor. The Mac is a nice geared motor, does most of what a Magic Pie does, but the gears make a little noise and will, in maybe 5,000 miles, wear down, along with the clutch. I run with Magic Pie at half the rated power, with a slow throttle ramp. Since the MP has no moving parts, it might last forever. I can ride my hubs with one gear, the gear I need to cruise at speed. I can throttle from a stop and pedal up hills with enough power. So you don't shift much with hubs, compared with mid-drives.
My gripe with the BBS drives is that they are fairly pricey. Bafang has no real competition for DIY. Beyond that, people end up putting fairly expensive chain rings on the drives, gear sensors, more expensive chains, and then rear hubs (IGH).
So, what's the deal with the BBS-02. Karl says there is a new and very different version, but no one is saying what they are selling and no one is saying if there is any difference in max power or whatever. There are clearly some different parts between the new and old. It is too bad in the sense that it was the safe way to go in terms of parts and You Tube videos to learn how to do stuff with the drive. It seems like a tired line of drives, anyway. Almost everything in DIY is static. I really like my hub motors but they aren't developing PAS systems and better ways to configure the motors and controllers. Golden Motors has a bluetooth accessory that works very well, but it is buggy and they never got the iOS version done, after a year. If the market wants sophisticated PAS systems and torque sensor tech, the DIY market is not doing it.