I’d say that for masks larger than 9x9 or 11x11, convolve_fft is probably faster.
Anyway, dealing with FFT has the property to consider periodic boundary conditions, which may not be desired. It’s still possible to simulate different boundary conditions by padding the original image, but if the mask is really large, this can be expensive (you have to add borders that are large as the half-size of the convolution kernel).