The use of ISBoxer is allowed; however, be aware that some of the features that it offers will breach the EULA/ToS, specifically, but may not be limited to, it’s the ability to use Input Broadcasting (1 keystroke send to all clients) and it’s ability to “cut” up the client to only show small part of it.
So what ISBoxer is usefull for is to divide your screen space up into sections, ISBoxer has various templates, which can then house a client each. For example have 1 main view (for the account in focus) and have several smaller “preview” of the rest around, clickable to switch focus to that client.