I like the fact that you can integrate credit card processing with your freshbooks account, be it paypal, authorize.net...etc.

Can you guys recommend some must have addons for client side management?

If you are using FBooks for invoicing, you are missing out on what a full-fledge accounting system offers you. Luckily, there is a very good one available for free. Check out Wave Accounting

Code:

waveaccounting.com

There is addon for Freshbooks but it is from Gravity forms, so u have to buy gravity forms or else if you can use nulled version, then you can find them in the forum in the download section. Let me know if you need the nulled version.