Built on T-34 tank, turret removed. 220 gallons of water gushing per second from two MiG-21 jet engines. This is one bad-ass emergency vehicle. Is it safe? Stuck in a burning building, I would be very happy to see it arrive on scene. Would I use it to take a shower? No.
I think repurposing an old Russian tanker is a great idea. It reuses something that takes up a lot of space. If it is made properly it should be completely safe to carry water and put out fires. It would be cheaper to use an old tanker than buy a brand new fire truck.
The engineers in Hungary are trained and specialized. If they made a fire truck from an old tank, it's probably even more safe than a typical fire truck. The Russian system had strong industrial capabilities, and that tank probably cost more than a typical fire truck cost to produce. The engineers probably reviewed specifications for the tank before releasing it to market, so it is reasonably sound and safe.
Honestly, I think while this fire truck is very cool, definitely and captures the vintage theme often used nowadays, it just doesn't feel safe. If I was to be rescued by that truck, I would be worried that it would break down, wouldn't be fast enough to attend an emergency and would be unfit for purpose.