TLDR: It works well.
I use a standalone FAT32 /boot partition (to make syslinux happy), and a F2FS partition as root. That does not matter at all though.
The kernel is passed
splash parameter and plymouth will do the job.
For syslinux, I set
UI vesamenu.c32 instead of
UI menu.c32, which allow flickerless pass from syslinux to plymouth.
MENU BACKGROUND #00000000 or a background image is recomended here.
But be careful with
MENU RESOLUTION 3840 2160, there might be strange stripes on screen when syslinux reset resolution.
To make it faster, you might set
TIMEOUT to a small value, and set
MENU HIDDEN, or just set
For the kernel,
vga=current i915.fastboot=1 will reduce flickers. There would still be flickers, but it is good enough.