Does this work to open sealed Mason jars?

One of the greatest inventions!! I've had one for about 20 years and yes it will open two part Mason jars, just take the ring off and it will pop the sealed part!

Is this only for first-time use before the vacuum seal has been popped or does it help make opening jars easier thereafter?

Hello! My name is Jessica, an employee at HIC Harold Import Company. Thank you for inquiring about the Brix Jarkey Jar Opener Original Easy Key. In regards to your question, The Brix Jarkey Jar Opener pops the vacuum seal of jar lids so they spin open freely, for first time use! Simply place Jar Key jar opener against the lid of the jar and, by gently lifting the handle, release the vacuum seal so the lid can easily be removed. Please feel free to contact me at jpetrecca@haroldimport.com with any other questions or concerns you may have to this product. Hope this was helpful!

Does it open screw tops

this is one of my favorite tools - it opens the kind of tops found on pickle jars, jelly jars, some juice bottle tops. it breaks the vacuum seal and the top then just comes right off.