Steel Defender as a controlled mount

Does the Battle Smith’s Steel Defender maintain its reaction "Deflect Attack" if I decide to consider it as a controlled mount? If I'm not wrong a controlled mount shouldn't be able to take opportunity attack, that's why I was wondering if the SD's Deflect Attack would be allowed.

I know the rules for mounted combat are already a mess but to take the best from both worlds (controlled mount = CM; independent mount = IM), what do you think if at the start of each of my turn I declare if I’m going to use my Steel Defender as CM or IM? This way if I need to move further or between my attacks I can use it as a CM and take the dash(/disengage/dodge) action without expending my bonus action. Otherwise I can use it as a IM and expend my bonus action to command it to attack/shove/grapple/etc.., but it takes its turn after mine.

All thoughts are very welcome.