Searching for something that might allow realistic hand-gun training to be conducted away from MoD or Police facilities, the P4 Storm is a fair choice. 

To all but the very well trained eye, it accurately mimics the Beretta 9mm/.45ACP original, right down to the Picatinny rail.  The weigh of this air pistol (without magazine) is similar to the full-bore weapon, as is the feel with a blow-back action that is surprisingly strong. Perhaps wisely, therefore, the P4 Storm has a very obviously smaller muzzle opening than its fullbore parent (in contrast to some others in the Umarex range where the end of the barrel is set well back from the actual muzzle).  

There are some other differences. For the pedantic, the more obvious ones are a moulded 'safety' (without red dot) on the top slide ...replaced by a slightly uggly but functional Umarex safety on the R/H side (above the pistol grip)... the lack of extractor detail on the RH side to the rear of the extraction opening, and a slightly odd looking aperture at the bottom of the pistol grip. This is to accommodate the  reversible magazine.

The magazine is worth separate mention. A very clever double-ended (2 x 8 shot) rotary design, it allows use of either pellets or steel BBs; BBs are held in place by concealed magnets (very neat!). Loading BBs is this very quick and, though pellets can be much more fiddly, use of slightly heavier domes with wide skirts can, with a bit of practice, be dropped very accurately into place.

So, another excellent Umarex product?  Overall, yes, but perhaps with a couple of reservations.  

Firstly, the rear sight is fixed. Whilst this will never be used as a target pistol, it would be helpful to roughly zero the weapon. On my example rounds fell (albeit in a very consistent group) off the left of the target (17x17cm) at anything over 15 metres. It would have involved little effort or cost to have allowed adjustment for windage as on the original.  The solution is to fit a laser dot sight to the rail, and use that.

Secondly, whilst the design is good, The P4 is built under licence in Japan for Umarex and the quality of construction, whilst fine, is not quite the same as its German built stablemates. It is a pistol that encourages hard usage and may fairly quickly result in wear that will effect operation; time will tell.