The pump part of these units is actually quite robust and will last for quite a time. The problem with them is the pressure switch. The cutoff pressure is set way too high on most of them (Most seem to be between 115-160 PSI). As a result the current being drawn at the point the pressure switch operates is quite high and the microswitches in them burn out quite quick rendering the whole pump useless.
I work with 70 PSI which is more than adequate for three storey work.
If you can find a workaround like fitting the 40amp relay as I suggested earlier or use a controller that you can calibrate the Dead End current with, you can make them last quite a long time.
They are great on trolleys as they are so light and you can run them off quite small batteries thus saving more weight.
On a van though I'd opt for a Shurflo.