I do own both of the machines you're asking about, but I am more than a little hesitant to consider either machine as being
guaranteed not to leak. Both are rated as waterproof - the Sport down to 10 feet and the MMK down to 15 feet (I believe - can't recall the exact rating). I can't be of much help with regards to the submersion thing since I have never submerged a machine (nor do I plan to). I don't dive, but I do wade in shallow water on occasion.
For me the MX Sport is the easier machine to use, but that is entirely the result of owning/using other Whites machines and a familiararity with the way the Whites machines work. The Multi Kruzer is not a difficult machine to learn or use, but (for me) it isn't as natural as the MX Sport is. I have to think about it (with the MMK) a bit more than I do the MX Sport. With time and use, that will disappear.
I'm short on time, so I'll mention a few things (off the top of my head) about each machine. The following is not the full list of features for either machine.
The MX Sport has programs such as coin & jewelry, relic, prospecting, etc.. A user can turn the machine on, choose a program, and start hunting (if desired) with no more changes. The machine tracks ground balance, but it will work better if the user ground balances the machine before hunting. Options include tones, discrimination levels, notching, frequency shift (for EMI). A new MX Sport comes with wired waterproof headphones (they're quite good in my opinion). An adaptor is available so other headphones can be used (that option won't be waterproof). The MX Sport uses AA batteries (
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The MMK has programs such as general, deep, two tone, three tone, and four tone. A user can turn the machine on, choose the program, ground balance, and start hunting. The machine tracks ground balance but works much better if ground balanced prior to hunting. Options include choosing one of the three frequencies, frequency shift (for EMI), discrimination levels, notching, tone shift. A new MMK comes with wireless headphones (not waterproof). Waterproof headphones (wired) are available. The MMK has an internal battery (same with the included headphones) that is charged via a usb port. There is an external battery holder (AA batteries) available for the MMK.
Both machines are very well made. Both machines are backed by companies that have stellar records when it comes to supporting their products (and customers).
The MX Sport is the heavier of the two machines, but it swings very well and is nicely balanced (my opinion). The MMK is lighter and also nicely balanced (my opinion).
Both machines can detect items at very good depth. It is possible that the MMK is a bit deeper (from what I've read) but I have not experienced anything that proves it to me. (That could be because I don't have nearly as much time on the MMK). Both machines are very sensitive and have good recovery speed. Both machines unmask very well. I think the MMK is the faster machine, but not by a lot.
At this point I lean a bit more to the MX Sport - simply because I have used it more and am more comfortable with it. I have no issues with the machine: it works extremely well. I like the screen (of the MX Sport) better than I like the screen on the MMK (its screen is very good though). I like the user interface (MX Sport) better - but that's because I am used to the UI of Whites machines. I prefer the sounds of the Sport - again, because I am used to them.
I like the ability to use one of three different frequencies on the MMK. I do like the UI of the MMK - it is relatively simple and you don't have to dig through sub menues; everything is right there on the screen. I love the wireless headphones - they're light in weight, comfortable, and not nearly as hot as the wired (waterproof) headphones on the MX Sport. I like the vibrate option on the MMK - enough so that I do not plan on getting the wired waterproof headphones. The MMK is better is salt water. The MX Sport is ok in salt water, while the MMK is excellent. I'd call it a draw in fresh water. I love the fact that the MMK can be updated by the user (via downloads made available by Makro).
The VDI numbers on both machines are fairly steady on good targets. Both machines can get a bit jumpy (VDI numbers) when the target is deeper. The stock coils (on both machines) are good coils, but I much prefer smaller concentric coils (for both machines). With the stock coils, both machines can be fooled by bottle caps. The MX Sport can be set up to discern the difference rather easily, while the MMK (for me) is not quite as easy to tell the difference (it gives a bit of a scratchy tone on bottle caps, but the tone is still very close to a clad quarter). Again - I think much of that is due to my inexperience with the MMK.
Assuming you're talking about fresh water hunting, I think either machine will be a great machine for your intended use. If you're hunting salt water the choice should probably lean more to the MMK. That's my take on it anyway. I'd hate to be without either machine, but I'd probably choose the Sport if I were forced to get rid of one of the two. Just because I know it better.
