The nicest feature of the MTAR is the position of the charging handle.
The position of the magazine release is nicer too - I supose - but not of huge importance to me. With the MTAR you could drop a mag with one hand while going for a new mag with the other... I could see a soldier possibly doing this in combat, but I keep all my spent magazines with me, so I will always reach for the empty first, so the TAR mag release works fine for my applications.
The MTAR optics rail seems to sit lower which I like.
The slightly lighter weight and shorter overal length are obvious perks to the MTAR.
I do however think I would like the TAR handguard better, and I would never use the extra rail-estate (oh thats a clever word) on the MTAR. The only thing I would put on either rifle are optics and a light - and the regular tavor is perfectly suited for that configuration.
Will I trade my Tavor for an MTAR? Maybe. It seems that the MTAR has some definite advantages over the TAR, but these advantages are not nearly as profound as jumping from say an 18.5" AR to the Tavor.
My 2 cents