Depends on what you're looking at.
One of the surplus U404.1's? parts are out there but pricey. Good luck finding mechanics to work on them as well. They are not simple vehicles, and some jobs like disassembling the portal axle outdrives require a bigger breaker and cheater bar than most shops can manage. Tranny swaps are downright interesting, requiring you to pull the cab and bed, then basically winch the rear axle back to get clearance. (Or remove it entirely). Even adjusting valves requires a special tool to turn the ball pivots for the depressors. Most have shielded ignition, and that means shielded plugs and cables. Not cheap or common. Overall engine access is cramped. Not as bad as some late 70's vans, but bad enough. The Zenith carbs like to vibrate themselves loose as well.
Surplus models are 24V electrical, the Swiss ones being preferable because they use circuit breakers instead of fuses, and tend to have better/more modern wiring. Most of the 404's out there seem to date from the 50's and 60's, with the Swiss ones being a bit later. Latest I saw was a 72.
Some, like the Belgian and German surplus ones have major rust issues, especially with the cab. The Swiss ones seemed to be in overall better shape, and had a cab/tilt that was more functional than the canvas mess MB came up with.
Dont ever expect normal road speeds, or "average" creature comforts. (The heater will either keep your feet warm, or kind of defog the window, but not both.)
If you think you're going to make an Ex Kraut radio van or ambulance into a super-duper camper, I hope you like 6MPG and a max speed of MAYBE 45 MPH on the flats. (And the potential of breaking down in the middle of Nowhere, Kansas with parts being scarce and expensive). The Swingfire heater usually found with these radio boxes does make a mean weedburner, but I'd seriously suggest not using it unless you really know them. If you can find one, the Swiss radio boxes are much better, with a safer combustion heater, and they are composite instead of steel and masonite like the German/Belgian ones. (No hidden rust issues.)
The municipal trucks are a little faster and a lot more expensive to maintain. U 406's were imported by Case for a while in the 70's, and U-416's and later series like 1500's and 1700's turn up as surplus occasionally. Even seen some of the U.S. "SEE" 'Mog tractors popping up, all with various issues. Great trucks if you have a spread of property or a small farm to maintain, and a source of parts and a competent mechanic.
You're basically buying a short range roadable tractor. Even the most basic cargo truck U404's are best thought of as a "tractor that can drive on a road" instead of as a "truck I can drive offroad".