Hi N3,
Yes 'Sandiebox' is a worthwhile program.
But like anything, it's not perfect and has been known to have been breached.
You should still use an AV and AM program.
'Sandiebox' offers an extra layer of protection in that anything downloaded runs in an isolated space which prevents them from making permanent changes to other programs and data in your computer.
Basically any changes made are discarded when Sandiebox is closed.
The good thing is that the protection that people get in the free and paid version is exactly the same.
The paid version allows you to create and use multiple sandboxes at the same time.
That way you can use separate sandboxes for different programs at the same time, doing so sandboxing/isolation works better.
There maybe more advantages of a paid version, but as i haven't used it extensively i don't know all the finer points.
What are the disadvantages if any?
Depends what you are using your system for.
If using your system as a normal every day computer...... not really any disadvantages.
If using you system to test programs/software etc ........ you may find it easier to use a VM.