some people swear by those devices, but I found it to be uncomfortable. I have not been able to use anything with a noose-type attachment for extended periods of time. Instead, I got the autoextender. It is working well for me. I use the vac extender during the day, and the auto exsleeve at night. They both use vaccum pressure to hold the weight on your penis, instead of a noose under the head. I have become accustomed to them, and wear some sort of extender almost all day and night.
I think you could gain 1 inch in a year or less, if you are totally new to PE. They call this newbie gains. Wearing an extender is one way that is recommended to cement gains and make them permanent. Experienced PE enthusiasts have told me that after the newbie gains, you could gain maybe .25 inches per year with dedicated work at PE.
I hope this helps!