Youre not the only one.. After my 10 year career on gliders, the managed descend mode is driving me insane on the 320. Especially if you for some reason, is high, the computer goes in total suicide mode, and vertical speed reaches values of 4000ft/min + which is not really comfortable, yet on the other hand, OP DES with the initial increase in indicated airspeed, due to Mach hold is not so nice either.. I have started to pull OP DES and select a speed target around 20 knots lower than our planned descend speed of 300 knots, and the profile is then constant (The captains that belives in fully managed think im crazy, but yet im one of the few F/O's which can land with the exact planned fuel from our CFP's - where managed descend on the same route, is around 200 kgs higher.)
I doubt that flight idle, is in anyway less economic, as you still generate thrust with the idle power, on ground.
