PULACO Ultra Quiet Aquarium Hang on Filter (66GPH 3W), Small Fish Tank Filter for 2 to 8 Gallons Fish Tank

Q: Would this work for my 1 gal. Tank

Too much flow for a 1 gallon. I put it in a tank that was 2.5 and the flow caused my fish to be pushed down

Q: Would this work for my 2.5 gallon tank? Or would this be too strong? (I have one beta)

Only if the back of the aquarium is completely flat and has a lip thinner than 1/2 inch (otherwise it won't fit). It is also very strong. I put it on my 5 gallon and it killed about half of my ramshorn snails in the first 24 hours. I woke up to them all stuck to the tube, dead. I returned it and bought a smaller filter.