Hi Emily,
you may use the web client also with your Standard or VIP account, you will see some more features in the drop down menues but may also notice, that this menues may not fit the size of the screen.. so you can't reach all points

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So the basic answer is: YES ..Webclients can be used to access all kind of accounts
BUT the Desktop Client gives you a lot of more comfort ... so it is a good idea to switch to it if possible.
I'm not a Mac guy... but running only Linux .. on both none Windows OS WINE is an option to run the WA-Software even without an installed Windows 'OS' .... but I can confirm it to work only for Linux.
If this does not work, you may set up a virtual maschine for example by running Virtualbox... either running a native Windows or a working Linux with WINE in it

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So there are some option worth to try ... but at least, the WebClient (and for Standard and VIP also the Mobile Client...) working fine with some hope to get the full client working on the MAC
So see you inworld
Quax