I have not heard anything except positive things about H&K's LEM. Even a die-hard Glocker said that H&K's LEM is like butta'. Todd Green at Pistol-Training.com thinks that H&K's LEM is mistakenly referred to as a double action but he insists it is a modified single action.
I must be honest and state that I have no experience with LEM. However, I do own a P30LS in V3. Granted I shoot it primarily is SA at the range.
At the gun store, you may find that the trigger has a lot of take up in single action; almost annoyingly so. But when you are actually live firing the pistol you will barely notice it and in many ways appreciate it because it's a service pistol; not a target pistol. You'll adapt very quickly just like you would with the clutch of a new car.
The target acquisition is very quick due to the sight picture that the large factory sights offers.
It is a highly, highly accurate pistol and entirely underrated. I am NOT a H&K fanboy but I will say this is one of the best service pistols I have shot and
I have shot Glock 17 Gen 3, Sig Sauer P226, CZ, Springfield XD, and Ruger.
Although a lot has to do with personal preference, two others who tried my pistol and shot it cold were also impressed by the accuracy and ease of shooting it. They were both accurate from the first shot. No warm up or "get used to" period required.
It does not have that harsh feel, and muzzle flip of what is stereotypically thought of polymer guns. It is a very smooth shooter. It shoots smoother than my CZ 75 and that's saying a lot!
Here they are:
I am surprised that the P30(s)/P30L(s) have been slow to catch on. I have shot a USP extensively, and my P30LS is much nicer to shoot due to the grip and controls.
The V3 in P30LS was just my personal choice as it offers so many configurations: Condition 1, 2, 3,...
For home defense, and bedside table insurance you might prefer the LEM because of its simplicity.