My 2 cents worth, put you money into stereo, if you have a stereo power amp, you can run one Marshall cab in stereo, just needs some simple rewiring of the cab. If you're up for it, I'll take you through it, I've got one of my 2 x 12 ADA split stacks wired to be mono (8 ohm) or stereo (2 x 16 ohm) using 2 x jack sockets (so just take one for rehearsal). One of the 2 cab jack sockets needs to be the shorting type (tip wired to ground when no plug inserted). Let me know what poweramp and cab your using. Or does your cab have a stereo switch, later marshall cabs have a stereo/mono switch (which is a different way to do the same thing as I've done but they include some speaker protection I think).
Personally, I've never wanted additional eq MP1/2, but some here are into it.
There are 4 main types of eq units But they all boost and/or cut volume/gain around a centre frequecy:
Shelf what you find in most hifi etc cheap mixers, basically divides the signal into bass and treb with 3 db dip in the middle where the 2 bands cross over, slope is flat shelf, all frequencies affected equally. But you can have more bands, e.g. 3 way shelf, Treb Mid Bass or 4 way shelf Trb himid lowmid bass
Graphic eq various number of bands (each band has a centre frequency (sometimes called Q) and a slope (the amount freq each side of Q are affected), slope is preset in the design, circuit). You can get 5 band to 64 band (i.e. 6th octave) graphics. Yours splits the frequency range int 10 bands and because it's an MXR they will be frequencies that relate well to guitar (as opposed to a PA graphic (mostly 32 band (3rd octave) designed to cover the whole freq range evenly).
Sweep eq lets you pick the centre freq that you boost or cut around, again slope set in circuit and are typically provided as the Mid band on low end mixers with Treb and Bass shelf
Parametric Lets you control 3 parameters, boost/cut, centre freq (Q) and slope (notch ^ affects narrow band around Q through broad, larger band around Q). It's unusual to see a parametric with more than 4 bands (Treb, HiMid, LowMid, Bass), but they are common on high end mixers and cost more...
All eqs sound different, I've heard flash ones that sound crap, and not so flash ones that sound good and everything in between (as a sound engineer I've bumped into many eq units)
Anyway hope that helps you understand if you even need one (IMHO you don't but each to there own
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