That has nothing to do with the Extension and everything to do with the hardware's program. The program must include a name. If the manufacturer has applied a name, all of the detectors from one manufacturer will most likely have an identical name, which would be good for filtering-out (assuming only one or two detector manufactures). If, on the other hand, each device you want to list is actually named, then you can filter-in those which may be much quicker if you know the total number of devices as you can stop the scan once the required devices have been found.
I doubt this is the case but if the devices you wish to find are always the same ones, then a scan of available devices is not required. The App can store the device addresses and simply connect only with them.
Concerning the number of devices being in the hundreds, that is bound to slow down a Smartphone because of the intrinsic design of BLE itself. Use a Clock Timer to allow all the devices to be found and added to the list.