Inara is brilliant and importing your frontier data is an absolute must in my view. Its worth it just for being able to see what materials you have and what you still need to collect for certain engineering mods.
I use EDDB to find out where certain commodities can be bought.
I think it can be tempting to use the third party sites for everything but I try to not let it take away from gameplay. For example, I'm currently scanning landable bodies in my home system and nearby systems for geological sites so I can bookmark where I can find G5 raws. I could probably get this info in a few mins from a third party site but its providing a break from the usual gameplay and giving me the excuse to jump in the SRV when I do find geological sites.
On the other hand, flying around trying to find the best price for void opals isn't fun so I'll use Inara for that.