Is there any caveat in speed as it seems here? Is openrc so slow?
Not for me
Boot speed is dependent on various factors like hardware, services started, etc. That video is kind of old, here is a newer one.
OpenRC for me is almost as fast if not faster than systemd as both have progressed with time (systemd seems to have added a lot of services like man-db, update-db, which can slow down the boot, while OpenRC seems to have gotten faster with newer releases) ;)
Alternative Tutorial to install OpenRC and eudev
Here is the link: Alternative way to install OpenRC and eudev on Arch