I use booster and it's cool. I don't see any noticeable difference in boot times but the image generation is much faster. mkinitcpio would take several seconds while booster takes about one.
First time I tried it it didn't boot because of something missing in the generated image. I tried a universal booster image (set universal: True in /etc/booster.yaml) and it worked. Technically this builds a larger image than necessary but it's still only 34MB and takes a second to build, so I never bothered to troubleshoot what was missing. The universal image even handles luks encrypted root partitions without additional configuration of booster (you still have to configure kernel parameters).
Another issue I noticed is that if you use grub-mkconfig and your only initramfs is booster, it will generate an incorrect main boot entry. It will add booster as an option in "advanced options" so your system is still bootable if this happens to you. The quick fix is to manually add the initrd entry under the main menuentry in grub.cfg.