UAC20 has 20% cooldown quirks. As long as you don't double tap they will not jam and you'll still get 25% increased dps over regular ac20. If you do double tap you can get more burst damage at risk of jams.
It's up for debate, some people claim that it can jam at a first shot as well. But, as far as I am aware the jam is checked when a trigger is sent for the second shot, before it fires. So, if you accidentally press to fire just before it finishes the normal reload, it may still jam after 1 shot (or if you accidentally click twice in rapid succession). It takes a bit of practice to get used to it though.
35% heat management on a brawler is really low, even more since Smurphy does not take into account the additional heat generated from successfull double taps. With ML you can upgrade to LE325 and have an overall better heat management... UAC20 should be your priority weapons and they are hot, so there is little point to fit MPL which are even hotter compared to ML (both faster cooldown and heat generated per shot) EDIT: you can even fit a STD 325 engine by losing 1 DHS