Another difference is that every team member needs a licence (needs to purchase) a copy of assets purchased from the Unity store.
The UE4 marketplace does not require this, for a team they simply submit a list of usernames who need access to a purchased asset.
Source: New Unity Pricing - Off-Topic - Epic Developer Community Forums
I’ve seen others use Unity store assets in UE4, but not sure of their official policy.
I know for sure you can’t use any assets created by Epic in other engines (all the samples etc), not positive if you can (but pretty sure it’s allowed) use UE4 marketplace items in other engines.
Here’s a quote from the Seller FAQ :
What can users do with my content once they purchase and download it?
All content sold on the Marketplace is licensed to the buyer (who may be either an individual or company) for the lifetime right to use the content in developing an unlimited number of products and in shipping those products. The buyer is also licensed to make the content available to employees and contractors for the sole purpose of contributing to products controlled by the buyer.
Each such product built using content purchased on the Marketplace must be a standalone creative work (such a game, simulation, or video) in which content is merely a component and not the primary focus. For example, it may not be a content pack for distribution to engine users.