Nikolay,The metal heater sure looks like it's the perfect heater. But it's not. I had one of them overheat badly, soften the hoses of the canister filter and the outflow hose separated from the canister. 50 gals. of water shot out of the filter all over the floor in a matter of minutes.
That was the time when I started to get paranoid about aquarium leaks (and dirty carpet too, haha).
But the Titanium heaters have round cables (easy seal with the plastic water seal gizmo part), not all heaters do.
That sounds like a nightmare of an experience! I can understand if you never want to use a titanium heater again because of it. However, it's hard to believe that the heater overheated because the body was made from titanium. It sounds like the temperature control was bad on your unit. The same thing could have happened with a traditional glass heater. There's always a chance that a piece of equipment will be faulty.
I've found that the Azoo titanium heater I used in the project linked above has worked very well. The two major plusses I've seen using the Azoo for an inline project are:
1. The temp control is separate from the body which allows you to not only see when it's on, but easily adjust the temperature.
2. It has an automatic shut-off if the heater is not submersed in water. A very good thing to have when the heater is out of sight, inside a pipe.