Some of them look interesting even though I've never used any of them either; like the LabelSync one for those who want a backup of their labels and a way to recover it again in another wallet, and there are some who want this.
LabelSync looks neat if you have wallets with many transactions and it would be a nightmare if you lost your labels. Not that long ago, some developers created a standard for saving wallet labels, where the data can be exported and imported among different wallets that support the standard. My guess is that Electrum will add that sooner or later. LabelSync saves your labels on a third party server in an encrypted format. That's ok, although possibly a little privacy infringing.
Labels are saved in your Electrum wallet files. But is there a way to only save the labels on your local machine without a copy of your wallet file and without using LabelSync?