Not that much more than sitting on a trailer. It's not ideal, but it wouldnt scare me going down the road.
The service brakes are all air applied. The spring is only for parking. I have only seen 1 axle per vehicle with the spring brakes (1 on truck, 1 on trailer) The ones with 2 clamps have a spring. The parking release pressure from the dash button is separate from the service apply pressure. I know this not from internet search, but because I changed them out alot. The ones with 2 clamps will mess you up if take the back clamp off! Why would you take the clamps off anyway? The typical failure was leaky diaphragm. You could take it apart and replace the diaphragm. That way you would not have to cut the rod on the replacement chamber to length. We had a heavy steel box with large slots to put the spring brake chambers in so we could cut the spring with a torch before throwing in the dumpster. They were afraid one would kill a garbage man or something. Also had to "cage" brakes sometimes to allow a wheel to move freely (usually on a trailer) the spring brakes come with a long bolt, you screw it in all the way and it holds the spring off. It's a pain in the butt. Probably 4" long and takes alot of effort the whole way with a ratchet.
Doesn't look like any more than one of the 5 wheel RV trailers.
