I suspect you currently have a limitation to the Single Interface, and that is great when your looking at that specific interface view, but as you rightly pointed out they have access to the other views and menu bars and will have access to ALL Nodes (albeit only that one interface).
I would suggest you add a Node Limitation for the Single Network Node of that device, in addition to the existing Interface limitation.
Edit - You could also remove the additional menu bars from that account to avoid the chance of accidentally clicking off that screen, and set the Home Page as the Interface Details page with that specific object:
i have done this already for home page view.. as i said, it works well, problem is that ther eis a hyperlink to HOMe which reveals a lot more info for the client.the problem is that the default summary view must somehow be there, it doesn't mater what it will be but you must choose anything. what i need is to give my clients their own log-ins, so they can view only their interface stats.
I had a similar use case and opened a ticket. The user to be limited could see the parent node even though account was limited to see child node and parent interface. I was told via my support case: The issue is interfaces are tied directly to their nodes even in the Interface table, so they will always be able to access the node, even if they have to manually adjust the URL to do so. At this time there is no way to prevent that. Even creating a Customer Interface view will show the Node name as part of the Interface name at the top [of the page].