RIM’s PlayBook is without a doubt, one of the most misunderstood and under-appreciated devices ever launched.

From its poorly planned debut and lacklustre feature set, to the dearth of available apps (compared to other platforms) and a lack of cellular data at launch, the PlayBook has had a rough ride.

But RIM isn’t giving up on the PlayBook –  as evidenced by the newest 4G/LTE version – and neither should folks who want to use their tablet for work and play.

Despite its shortcomings, which incidentally are fewer and fewer as time goes by, the BlackBerry PlayBook possesses two features that make it unique in the tablet landscape. One of those features is the ability to tether your BlackBerry smartphone to the PlayBook, giving you full access to your BlackBerry’s features but on a much bigger screen.

The second is BlackBerry Balance. Balance lets you create a complete separation between work and personal tasks on the PlayBook, a truly outstanding feature that neither Apple’s iOS or Google’s Android platforms have been able to deliver.

Sure, you can enable parental controls on these devices, but these restrictions disable apps completely instead of creating a virtual wall between work and personal apps. It’s the baby-sitter or nanny approach to control.

With BlackBerry Balance, once you’ve indicated that you want to create a “work” container, you can lock the Messages, Contacts, Calendar and Work Browser with a single password. Once locked, these applications are no longer accessible, but the rest of the tablet’s apps remain available – even a secondary instance of the web browser for personal browsing.

This ability to put all of your sensitive work-related info behind a locked door is a boon to families and anyone else who finds that their tablet ends up being passed from one person to another. RIM’s realization that our tablets – even more than our phones –  are becoming shared devices, is a brilliant insight.

It’s not without flaws, however. The first being that in order to use BlackBerry Balance, you need to connect your PlayBook to an enterprise email account which is running RIM’s proprietary software on the back-end. If you just use a blackberry.net email address, or a POP email account like the one give to you by your ISP, the feature isn’t available to you.

Balance also plays somewhat heavy-handedly with your locked apps. For instance, if you have a work account and a personal account set up in the Messages app, once locked, you can’t access either. RIM needs to (and claims to have plans to) find a way to only lock that which is work-related, leaving all personal data accessible.

These limitations notwithstanding, BlackBerry Balance is easily the most compelling and unique feature on the PlayBook. I doubt it will be long before Google and Apple catch up, but in the meantime, RIM has a killer app on their hands.

At a time when the company is holding its breath for the next 4-5 months until it can release the promised line of BlackBerry 10 devices, it needs all of the help it can get.