Armaguard are progressively switching over to the Beretta APX
http://www.beretta.com/en-us/apx-striker/ as their staff roll through their annual requalification course.
As to why they used revolvers for so long, the answer is simple. Cost. Armaguard (and Prosegur, formerly Chubb) have thousands of firearms between them and revolvers were the only option when they got going. Despite the advances in firearms in the intervening years there has been no great incentive to upgrade to semi atuos when there is no real benefit. The pistol is mainly a deterent and a last chance option if the guard's life is threatened so there is no need for bigger ammo capacity, speedier reloads or anything else a semi auto does better than a revolver.
The cost for Armaguard to upgrade to the APX is in the millions and they are getting the guns very cheaply as Beretta has gained no noteworthy contracts for the APX which was entered in the US XM17 Modular Handgun System trials that resulted in the Sig P320 winning. I would say they finally swapped over as the vast majority of their revolvers are all exceptionally old and they finally got sick of rising maintenance costs combined with the difficulty of finding someone to service them all. I know when I was there they didn't use either Nioa or Grycol, the Ruger and S&W importers respectively) for their servicing needs. I assume the APX contract is much more detailed and would include an overall package of magazines, parts, servicing and support as opposed to whatever the deal was thirty years ago when they bought their old revolvers.
In QLD at least, the training for a Cash in Transit guard is no different for revolver or semi auto as far as security license holders go. There is a certain number of shots at a target from set distances (maxes out at 7m from memory) and all shots must be within the human silhouette. The course of fire involves strong and weak hand shooting but most is shot with two hands. The course of fire also involves a couple pf mandatory reloads ie shoot a couple of shots, reload, shoot a couple more. The course is not hard for someone who shoots even semi regularly however over 95% of guards have no interest in shooting and do not have a target license or any other experience shooting handguns.
The initial course takes about a week but most of it is to do with when you can and can't shoot, deescalating threats etc. There's a couple of days of hands on stuff with a max of about a hundred rounds shot including the actual qualification shoot.
Guards can only shoot to defend their own life or the life of another, they can not draw just to protect their cargo. As in any other industry where robbery is a concern the first thing to do is obey the attackers instructions and comply. The reality is most robberies end in no shots fired and the chance of a running shootout is virtually nil unless the guards go rogue and decide they are John Wick all of a sudden. As someone else mentioned you can't cock the hammer on your revolver either. The only time you should pull the gun out is in an imminent threat situation and if you had time to draw, cock the hammer and fire you were not in imminent danger. If they can prove you cocked the hammer you are toast.
Source: I used to work there and still have mates that work there. I kept my security firearms license even though I don't use it as it cost me a few grand to get by the time you include the security course, security license and firearms course and license. I actually have a requal due in the next couple of months.