Paul,
I have the same version. The harmonics are sufficiently down on 30 and 20 but it was recommended to use an external LPF on 40 as the harmonics appear on 20. Myself, I never used a 40 LPF but also never used an amplifier. If your amplifier has a LPF for each band, you probably will be OK using it.
Gary
W9TD
Gary W9TD