Be Careful!!!!!
Using V/S is OK...but, you have to watch your airspeed. You can't set Vertical Speed and go back to reading your newspaper or magazine. You could have unacceptable airspeed excursions.
With regard to Managed Speed and the uneven climb rates (sometimes drops to Zero for a moment or two), Airbus says that's OK. It's still the most efficient (based on your selected Cost Index).
Personally, I like to use Managed Speed when all things are wonderful. But, throw in turbulence, or ATC requests/requirements, etc., etc....I may have to resort to V/S.
Another method is to Select Speed/Select Mach to something a bit slower (not too slow), to give you a short-lived boost in the pants. This works...depending on your immediate requirements.
With regard to the 500 FPM minimum...it is not a minimum climb rate...You can climb at only 50 FPM, if that amuses you. It's just that anything less than 500 FPM requires notification to ATC. In the case of momentary drops in climb rates in the Managed Speed profile, ATC need not be notified, unless the drop is more than 'momentary'. This is up to your judgement...what ATC calls to make..., captain.
Hope this helps....
PantLoad