Unfortunately, it's been nearly impossible for many months to find LEM kits anywhere. So there's that. You can find most of the individual parts from HK, MGW, and Numrich. The one part you will not find right now is the LEM axle (214258), unless someone around here has spares they want to sell (if so, I'll buy!).
As my screen name might suggest, I'm a huge fan of the LEM trigger. It's certainly a polarizing trigger mechanism. I like them for several reasons.
For one, in the USP series, the side-mounted safety levers compromise grip. I am all about performance when it comes to grip method. To me, that means an aggressive and high thumbs-forward grip. The safety lever gets in the way of that with your primary hand. If your primary hand grip is compromised like that, it forces your support hand to be lower than normal and then you see a reduction in consistency and performance with your recoil control and follow through. This isn't subjective, and you can see the difference if you measure it with a shot timer.
Another factor, consistency. The transition between DA and SA pulls can be trained, and it's not a huge deal to get used to that. I've shot SIGs and Berettas for years, though I've been shooting and carrying Glocks heavily for the past ~15yrs. I have a high degree of reps on striker-fired guns. It's an ROI thing. The LEM trigger feels a bit like a much longer striker-fired trigger. I don't have to think about it, I just pull it, and it's the same with every pull. Additionally, no need to ever mess with decocking, so one less manual of arms.