Depends both on the betta and the fish he shares the tank with. He might be e little psycho, or they might be fin-nippers. I wouldn't keep a betta with tiger barbs; they're much more active than bettas and I would be afraid the betta's long fins would be too tempting for the barbs, even if they were in a school and mostly picked on their own.
The heaters that come with these kits are submersible. The water line indicated on these are the MIMIMUM water line. If the water goes below this level your are at risk of having an exploding heater. Just thought I'd investigate a little because your questions made me look into my own. This is why it is pictured horizontal and submerged on the box.
