1. Worked fine, used mksq_opt="-comp lz4 -Xhc"

2. This was the only available option in mksquashfs for lz4, it does it's own thing and options available in the compressor are not all available when used in mksquashfs. I'm assuming the "Xhc" is it's way of using the lz4_hc variation that compresses more than just using lz4 does.

3. File size compressing 2.63 gig system: Zstd=859 mb  Lz4=1.1 gb. So it's quite a bit larger, Zstd is already about 10% larger than Xz, Lz4 is about 40-45% larger than Xz, so it's a non-starter for my use as the file size is just too big.

4. Lz4 even at the high level I used, is MUCH faster compression, it took about half the time xz does, and a third of the time that zstd takes.

5. It's snappy as it can be in live-session use, but not sure there's much of a gain over zstd when all factors are considered, I still need to test an install with it to see if that's any faster, but the Refracta-installer on the zstd versions is so fast now it might be hard to tell any difference there either.

6. All in all zstd seems to be the best balance for everything but compression time where it's slow as molasses at high compression rates.

7. But if you are in a hurry to roll up an iso and don't care if it's larger, lz4 is the clear winner for speed even at it's highest compression level.