Absorbtion refers to ... well .. absorbing sound, which usually translates to reducing the echos in a room.
Isolation refers to keeping a sound trapped in a room, also known as soundproofing. It's very, very difficult and very expensive to create a truly soundproof space, but it's not very difficult to create a deadened space (not very much echo) suitable for a recording vocals.
The product in the link you posted would work, but you could do it for much cheaper if you're willing to do a little work yourself.
You can buy 2' x 4' x 2" sheets of 8pcf mineral wool that will absorb the sound very well, and these can be bought for around $4 or $5 a sheet. Then you can cover them with fabric (or frame them with 1 x 4s or 2 x 4s and cover the whole thing with fabric) and attach them to the walls on the inside of your booth.
The problem with using carpet is that it only really absorbs high frequencies. The mineral wool (or 703 rigid fiberglass, which is another popular choice but more expensive than the mineral wool) is a broadband absorber, which means it absorbs a wide range of frequencies from treble to bass. They don't get the really low bass, but the voice doesn't usually generate frequencies that low anyway.
A place that carries both the mineral wool and 703 rigid fiberglass is SPI. (
www.spi-co.com) They've been really helpful when I've worked with them.