I had this, unbaffled, on my 5.5 gallon and I agree that it's just a bit strong, particularly for full finned boys, but it does help to have it submerged. I added some cherry shrimp to that tank and I was afraid of the little guys getting sucked into the filter so I "upgraded" that tank to different filter and luckily had it as a spare when the filter on my 3.5 gallon died last night.
I put the i25 into the tank as a replacement, but I was afraid of it being much too strong in such a small tank so I easily baffled it by using a rubber band and attaching a piece of filter sponge media to the outflow area. There's just a very slight movement to the water, only noticeable because of the gentle movement of some floating plants.
My little plakat boy loves his tank.