The most obvious pro is that you can see through them so it’s a ton easier to line up the stamp the way you want it. They are also unmounted, so it takes a lot less room to store them. The cling is built in, so a dirty stamp just needs washed to renew the cling.
Some cons are that the images aren’t as detailed as traditional rubber stamps. If you have a long border, it may also be difficult to place it exactly straight on the mounting block.
Whether you choose acrylic or rubber stamps and care for them properly, they will each give you years of enjoyment. You can find out more details about acrylic stamps here: Acrylic Stamps: Are They The Best Choice For You?