Yes. You'll be missing out on a some stuff...that you likely don't use. Propritary security features is a big one. Propritary backdoors. Actual validation of all the features has not been done unless the oem enabled coreboot.if it was not the oem, it's only functional validation which can bring out corner cases. With a MB that old, I'm not familiar enough to speak about specific features that would be missing.
If you are a generic computer user, you will never know the difference other than a quicker boot and different splashscreen.
I'm a fan of coreboot.
Yeah, I don't have that option on jerboa and loading lemmy in a browser on mobile is a terrible experience.