Now, I personally have had two builds with LM. One with LM as the material for a CPU re-lid, and another for a direct-die application. Neither touched aluminum or untreated copper.
The re-lidded CPU is still going strong, no issues. But with the direct die application, I found the performance to significantly degrade after two years. Apparently there's a pump-out effect.
I ended up switching to PTM. Same temps as LM, but zero degradation so far.
Although I've never been conscious of pump out as a problem, and have never reapplied thermal paste, I did use a KryoSheet on a 9800X3D in my most recent build. So far, so good.
But it was a very informative video regardless.
https://www.youtube.com/watch?v=rNjoREOH80Y
He's a beast at BGA replacement, if you want to learn how to handle big chips he's the one to watch. But yeah, liquid metal sure seems to kill a lot of them, though typically just for the prosaic reason of getting somewhere it shouldn't and shorting something out.
Both seem to regularly face laptops and GPUs respectively that have BGAs shorted out by leaking liquid metal.
I don’t think I’ll put anything liquid on my electronics ever again.
FWIW, you can set it horizontally. You need to use the -heh- stand they include for the purpose, but it's how I have mine configured and it works fine.
I get that size and shape of the case may make this the least popular way of orienting the hardware, but -unless they've decided to save ten cents by not including the stand- it's just as doable as the vertical orientation.