they are the most common and cheapest. but they are still okay. i had 2, got rid of them. all they did was chase eachother around when i shut the lights off. and my sweetheart(JD) would constantly chase the bigger one around. he was so scared of her. now on the find a NGT to go with my NTT. or maybe a ST. or maybe all of them(no AT's of course). now that would be a sweet tank.