Is rank requirements only for getting items, or for using them as well, on Vanguard, Crucible and Eris?

For some items on vendors where there is a rank requirement before I can purchase the item, does this rank requirement apply to:

• Only purchasing the item
• Both purchasing and using the item

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Background

I am playing a level 31 Warlock. I want to do the Nightfall, Weekly, etc. more than once each week and get rewards.

If I create another Warlock, level him up to 20, can I then shuffle all my gear from my current one onto the new one and level him instantly up to level 31, with good weapons to boot?

I ask because for this new character, some of the gear will have been bought on vendors where there was a rank requirement, like getting Crucible vendor to rank 3 before I can purchase weapons, as an example. Will such a weapon be usable at all on this new character with his lower rank on said vendor?