It shoudlnt be a problem i use a small fluval filter for my 10 gallon and the flow isnt that much to be honest but im not sure what it would be like in a 4g??
But I have a betta who seems to seriously enjoy gettin blown around by the external filter outlet, each to their own i suppose.
I'm would advise against all of those most betta people worry about the flow from a hob filter useing a internal power would be bad. Just use a sponge filter their cheap and work great, if not look for a small Hang on back type
Unfortunately the +1 is the only one of the range that does not have an adjustable nozzle but the flow is really nothing to worry about. It doesn't even agitate the surface unless the nozzle is above water.