I had a terrible experience trying to import my Facebook contacts to my iPhone. I thought that would improve things. Nope. It did the opposite
Maybe this is related to the fact that i have many contacts. Maybe not. All i know if that i used a popular (apparently well done and rated) app called SmartSync that is supposed to match your contacts in your iPhone with your Facebook contacts and enrich it with photos, numbers and emails you don't have or that are not up to date
This has created a massive mess. Right after i used this app my iPhone was burning hot. Every app was crashing. i suddenly got double the number of contacts with a lot of meaningless "No Name" Contacts. All my contacts are backed up in iCloud. I tried to remove the iCloud settings. Crash.
I tried to reset my iPhone to a previous iCloud back up. that would not work and the iPhone would crash on the way.
I knew this was because of the contacts. I had to find a way to clean the mess
I merged the duplicates and erased the empty contacts: i did it from my iPad which is synced via iCloud with my iPhone. Things got back to normal
So now you know. Avoid the Dumb Sync
So far the very best tool i know to enrich your contact book is by far WriteThatName