the reliability issue is simply from personal experience...not gleaned from any text, report, or study...
we had access to both a and b model uzi's in the weapons pool a million years ago when i was still calling myself a soldier (special operations unit)... granted the weapons were old and had been beat up alot, but they never performed to the level that our mp5's did...
even had a couple of sweedish-k's, and a couple of SW76's there... trained with them all on occasion..
a couple of years ago i had the opportunity to a/i a "tactical submachinegun" course for a small police department in northern illinois.. their tactical team was still carrying B models (i think they still are today).. several thousand rounds down range per weapon that week...
as a current team leader with a metro area SWAT team, i work with mp'5 daily (have one issued, as well as an m4)...
just happen to have a decent amount of experience with all the weapons systems named (most have to rely on what they read in a magazine, what they have been told, or base their opinions on limited experience with different weapons).. its been my personal experience that while the Uzi is a robust weapon system and is not prone to breakage or failures like so many other open bolt sub guns, it does experience more problems than the mp5. problems with the Uzi's inclulde (while somewhat uncommon) "run away" guns, when they have been subjected to alot of continuous or full auto fire, and spring breakages..
again, this is NOT meant to say that the Uzi is unreliable.. it is far from that, and is my 1st choice if i am required to use an open bolt sub gun (thankfully that is not the case).. it has simply been my personal experience that it isnt as solid a system as the mp5
(not that it matters, and i recognize that i am probably PAINFULLY lucky on this, but ive been shooting mp5's off and on for close to 15 years now, and i have NEVER had a malfunction with one... not one.. ive obviously seen them, but have yet to have one of my own...)
Stay Safe and Win at All Costs!
Dave West
www.legionconsulting.com