There are those who run filters in their betta's home successfully. If you look into it further, you will find that people have taken special measures, made specific adjustments to their filtering systems in order to slow the current. Some may decide to keep their betta in a large sized tank, for example, 10 gallons, which leaves the betta plenty of space to retreat from the brunt of the current. This is especially important for the males. Because of their long fins, they have a harder time maneuvering around in a tank with a strong filter current. As with any circumstance, there are always exceptions. Some have kept male bettas that actually enjoyed playing in the brunt of the current. Again, this is the exception. Generally, the males will most definitely shy away from a strong current. I once had a betta that would stay hidden in his hidey when I ran a filter. Once I realized it was not going to work out, I moved the betta to a smaller, filterless home where he happily lived out his life span. The female bettas, they do better by far in filtered tanks. Their bodies are more sleek and streamlined to better maneuver through the current.