So with a bonded object for a wizard, if I don't have it available, I have to make a concentration check to cast spells. Would I have to do the same for spell completion items like scrolls?
You can't use items like scrolls without having them in your hands (you actually have to read scrolls, not just hold on to them.) You just can't cast the spell without actually pulling the scroll out.
The rules for bonded objects are specifically about how wizards interact with magic and shouldn't be used for other items.
I'm aware that I need to read the scroll, but from what you're saying I'll be able to cast spells unhindered without my bonded item
No, your bonded object limitation only applies to spells you're casting. A scroll is still a magic item that you activate. Different thing.
Thank you for clarifying