Aye Up,
If you look closely you will see that most folding shovels have the blade attached to the hinge by way of solid rivets (I've seen some that are hollow though!).
This means that a
sheer line is created between the blade and the hinge
at the rivet - an inherent weakness - everytime that you thrust the blade into the ground you are effectively trying to guillotine the rivets!
Depending on how good the rivett steel is and how frequently/hard the shovel is used the rivets eventually work loose and in some cases fail. I've seen this many times with the cheaper folding versions but also on one occasion with a German folder (loosened rivets that is) - but it had been abused by way of hacking at roots and rocks.
If you look at the Gerber you will see that the hinge is welded to the blade, eradicating the rivets leaving only one sheer point - the hinge pivot. On the Gerber the single pivot bolt is quite substantial and is replaceable should it suffer from wear (I suspect though that the hinge slots would probably enlarge first.
I've owned the Gerber in the image for the best part of 20 years, it has been used in anger many, many times and apart from periodically re-sharpening the blade mouth (for digging!) it is still in extremely good condition.
Of the three types of handle available - 'T', 'Y' or Straight, I have found the 'Y' as per the Gerber the most comfortable for prolonged use.
The 'T's are often the first to break and the straight handles can cause blisters as you have to constantly grip the shaft as you drive the blade forward, especially if digging in moist/wet sand. (best practice - use field gloves!)
The weak part of the Gerber I suspect will be the handle if it is not used correctly.
The advantage of the German surplus over the Gerber type might be the pick - but a small pry bar carried with the Gerber resolves that issue.
Of note, about 3 years back I picked up an identical one (in design and folding method) at a supermarket in a box with the AA (Automobile Association) logo on it. It was very cheap, less than a tenner I think. I bought it as a spare. Compared to the Gerber it looks marginally less well put together and the plastic may well be of a lower quality (only use and time will tell) but used correctly I suspect that it will be better than the cheaper alternatives.
Just did a quick Google on AA shovel - still available £8.99 at the mo. They advertise it as a snow shovel - hardly, but we've covered that already.