I researched this quite a bit last summer and the general consensus seems to be that most people were able to use cards even when inside the sleeves, so they aren't worth much. Things like ID badges to unlock doors unlocked 'em even when inside the blocking sleeve.

I have a CC in a sleeve. I think they are really intended to protect you when standing around nefarious folk. But yes, at a checkout you might be at risk. Aren't the new chip CCs supposed to not need RFID sleeves? Or am I mistaken?

I have a metal lined one that I use and yes I like it. Of course you could line your wallet with aluminum foil lol.

My hubby travels a lot so he uses one. We also have a paid protection plan. Our cards all have the new chips, but sadly not every store uses them and even the ones that do, their readers don't always work.
You might find some helpful information in this video too.
http://abc30.com/shopping/keeping-holiday-shopping-fraud-free/1097034/
I also watched another video showing how aluminum foil can block a cell phone getting a call. Supposedly they can't get the radio frequency they need to receive calls. Not sure if that's how the RFID readers work, but if so I'm thinking good old aluminum foil might be the easiest way to go.

I have 2 - one is a passport holder with 8 credit card slots on one side and an id slot on the other for a driver's license. The other one is a wristlet that will hold my cell phone too I didn't purchase them because they claimed they were RFID blocking but because of their features.

Unfortunately the opinions as to whether you need one or if they really work seem to vary widely. One of the things that confuses me is that the chip cards are advertised as offering greater security - but all of the ones I have also have the swipe feature - so doesn't that still make them less secure?

I thought this article from Slate was interesting;

http://www.slate.com/articles/life/travel_explainer/2015/08/credit_cards_passports_and_rfid_fraud_are_special_blocking_wallets_necessary.html

I ordered a bunch of cc sleeves from amazon...very inexpensive.

Maire, I noticed that too about them having both the swipe and the chip. I think it's because not all businesses are set up for the chip, and as I mentioned above, even the ones that do, they don't always work.

I have an expensive little metal card case/card wallet that is a blocker. It has an accordian inside where the cards fit. Something like $8. Does the job. I keep money and id separate.