I've had mine for about 1 year now. Still learning it though - much of that is due to using my other machines instead of really putting my efforts into the MMK. It isn't a difficult machine to learn, but (for me anyway) it's enough of a change (from my Whites machines) that I have to think about what I'm doing when setting it up for a hunt.
Well built machine. Light weight, swings nicely, and is well balanced. Fast recovery (3 tone) - does a nice job of unmasking targets in trash. 4 tone is deep, but a bit on the noisy side of things. Does very well in salt water, but probably not the machine for dedicated salt water hunters. Stock coil is a good one but I prefer the 7 inch concentric coil.
Bottle caps often ring up as quarters - but the tone is just a hair off (stock coil). Wiggle the coil back to the edge of detecting the target and a bottle cap gives a broken tone (kind of an iron grunt) prior to giving a quarter tone.
I have dug a number of good targets where the hole had trash objects above/below/near the good targets.
Love the included wireless headphones. They're so much better (IMO) than corded headphones. I do not own the waterproof headphones and do not plan on getting them (I don't hunt in water that is more than a foot deep - or thereabouts).
I'm not a fan of the pinpoint button placement - off-center to the left side of the face as you're looking down at the screen - but the pinpoint function works quite well.
Changing modes, settings, etc.. is easy and you don't have to dig through menus to do so. I do find that I must pay attention though, as I sometimes end up changing something that I wasn't intending to change (hitting the wrong button, by mistake). Again, that is due to my being familiar with my Whites machines - not a problem with the MMK.
I did purchase the external battery holder, but haven't used it. Thus far the internal battery life has been very good - far exceeding my willingness to hunt until they run out of juice. I really like the internal battery - no batteries to buy and I don't have to fumble around putting batteries in a holder each time I want to go hunting. I do have to remember to charge the machine/headphones if I have been using it a lot - or haven't used it for quite some time - but that hasn't been an issue thus far.
I did do the first update - that proved to be very simple and easy - but have not done the second update (it doesn't offer anything I am interested in).
I am very pleased with my purchase.
