I upgraded from an Ascaso i-mini to a Macap M5 when I owned a BZ07. Then further down the track, upgraded from the BZ07 to the VBM.
Did I have to upgrade from the i-mini to the M5? Depends. If your concern is simply for a grinder to grind fine enough for the VBM, then i-mini and the likes will be fine. But if your concern is about whats in the cup, then in my opinion, the M5 and its likes are a minimum - if you can afford it, go even better. Makes a huge difference like you wouldnt believe.