I like the flexibility that the Lexicon MX200 gives you with different routing options, separate lights and more controls for each channel independently, and most importantly, it has real presets!
Although the M350 says there are presets, I don't really consider them presets.
The M350 definition of preset is: set each knob to 12 oclock and then try each effect.
The MX200 definition of preset is: Preset #1 is already tweaked and saved with all knobs already set (pre-set!) to give you a Big Pop vocal sound, #2 is pre-set for... etc..
There's a list of 99 of these telling you what the preset is good for and you can save 99 of your own.
For someone who doesn't like to tweak, the presets on the MX200 are great, for someone who likes to the tweak, MX200 gives much more options and flexibilty. I found the presets really help as a starting point with something that already sounds decent and you just tweak it to taste. When I had an M300 (M350 predecessor) I had a hard time getting good sounding effects out of it (granted that I may not have known what I was doing back then
, so I sold it and got the MX200 and at least it had presets to get me going with something that sounds good. And yes, the MX200 does have tap tempo.
I also like the MX200's Librarian program that you install on a computer and connect to to the MX200 via USB.
It shows you the exact settings of each preset so you can get ideas of what they've done to make that particular sound
and then can edit it to make your own using theirs as a starting point. I do find the MX Librarian is alitle quirky, though, and I haven't found it reliable for live use, but for seeing/editing/setting/saving presets it is useful.
Just some reasons why I like the MX200 over the M350.