You need to combine manual exercises with devices for the best and the fastest gains..if you only use the follosan forte ( or any other device alone with no manual exercise ) it will take a very long time...the best way to gain is to combine manual exercises with PE devices..If you only want to use phallosan to gain 2+ inches i'd say it will take a few years.
The Phallosan is too young at this point to see those kinds of gains but I am sure they will happen as time progresses. I think so far the biggest increase, using the Phallosan alone has been 1" and this happened over about 12 months. I will try to remember who this was and I will post a link to his progress thread for you to see.
Gaining two inches is far easier using the SRT routine, which incorporates the Phallosan along with exercise and other tools to produce the fastest gains and the most productive healing time. There is also a 24 version of the SRT that I wrote but no one has tried that yet.