Has anyone tried these SnugPlugs?

An electrician friend of mine said that they will ruin the outlet. Over time the contacts writhing the outlet will be pushed back and loose the ability to hold a plug with or without them. For 3-5.00 it’s best to replace the outlet. If it’s a heavy use outlet buy a better brand, e.g. Hubble

I would want to know how they change the sound before I decided on using them.

I think the concept is prolonging use of an already ruined outlet

Go for a better outlet.  I noticed a bigger improvement in sound over new a/c power cords.

For $10, I'll just buy a good outlet. 

Put "audio" outlets on my 2ch and HT setups, even changed my bedroom one. The new outlets hold cords very, very well! It's hard to plug in, and even harder to unplug. Did not go crazy on outlets, they were around $30 each. 

Sadly, most house outlets are dirt cheap bulk items, you know the 20 pack for $10 kind of outlets. They do not last, and are crap to begin with. If you replace them with good outlets that cost $2-5 each, they will be a huge upgrade. 

On my house, they backstabbed most outlets. Just changing that was an upgrade.