I mean it's a trade off between "how durable do I want it to be". A bren carrier one shot by AT guns and 2 shot by most anything else.
The buffs it provides alone are worth the cost. The recon plane is just icing on the cake.
With how early you can get a bren command vehicle, it can get pretty nutso.
In the later stages of the game, I don't mind putting it on a Centaur since I generally want one as an AA platform but it's not a front line combat unit later in the game.
i agree that it's a powerful tool, the problem is that if you use it on a centaur for example, it's now super shit against infantry and even more vulnerable. i can't justify spending ~~100 fuel just so my command vehicle doesn't die in one hit; i'd much rather have to buy 6 bren carriers (6*15=90) fuel, then use it on an actual tank. even late in the game (team games) i still use my centaur to fight infantry. heck, i use the wasp lategame if it survives although only from behind shot blockers.
just to be clear, the commander ability itself is awesome, particularly for the recon plane, but i just can't justify putting it on a tougher platform because it makes that platform combat ineffective and vulnerable.