I can respond about leaning the fuel at altitude.
First, you do not need to be in closed loop. As the fueling is selected, it originates in either the IAP (intake air pressure) mapping or the TPS (throttle position sensor) mapping. It's is then trimmed by inputs from the differential of the intake air pressure and the atmospheric air pressure sensor. intake air temp and coolant temp sensors also play a role at this point. so if you go up in altitude, the differential of pressures is already considered and applied. If the ECU didn't have a method to compensate, fueling would be all over the place as the vehicle is ridden at different altitudes.
Additionally, Since these inline fuel controllers go in between the ecu and injectors, they can only rectify the injector pulse, but they don't know which map it's originating from. I have no experience with the Dobeck unit, but power commanders are impossible to map at low throttle settings because they are working on correcting the TPS responses, and that's why folks complain about flat spots and hesitations in low throttle settings.
Also, Fuel mappers are limited to that... mapping fuel. There are other controls that impact how the engine runs and responds. Timing is a big one. It can be changed with ecu flashing, and not with a piggyback unit. Likewise for secondary throttle mapping changes. My flash has a full complete rebuild of all these maps and they aren't even similar to stock. That's why the throttle pickup from closed is as smooth as it is. Good secondary mapping coupled with fuel cut delete, which is another thing piggybacks can't do. They also can't shut off the 02 sensors or pair valves / CEL lights, change the rev limiter, etc.
Finally - fuel economy. With flashing, you can target individual cells all across the map, from idle to redline. When building a flash, I not only use a dyno, but also I ride and datalog extensively. the bike is hooked up with a wideband 02 sensor, and it's recording the relative afr's for each cell. because of this, I can change afr's depending on the use. light throttle is leaner than full throttle. I generally DO NOT autotune. In this manner, excellent fuel economy can be maintained. Piggypack units, at least the pc's, can be autotuned, but you need to know what you're doing, and it's more of a "batch" change than a cell specific adjustment. If you're just adding 8% fuel all over the place, well, you're not going to get the best fuel economy. Booster plugs are really bad for this, but if it's all you've experienced you think it's the best.
Technology has marched on, and the booster plug and piggyback fuel controllers that are "tricking" the ECU data have fallen by the wayside as ECU access has improved. Now we can go to the source of the data, and change it accordingly. We can't get stuck in a time warp. What was good a few years ago has been passed by with this new access. If you want to be good at tuning, you have to keep up. it's not easy, and I for one am constantly learning.
I hope this helps.
Steve