I don’t hear any tone suck with my Zulu+ dialed in using the key input with the serial effects loop of my Mesa Boogie JP2C. For high gain rhythm tones, it sounds awesome. For leads, I click it off just because I like to sustain notes longer than what is optimal for rhythm settings.
That’s what I did - bought a used H&K 412 dovetailed birch ply cab from Guitar Center for $125, shipped to me for $25, installed better speakers, sounds awesome.