One thing to consider though...
Recently B4A version 2 was released, it was the first version with support for user-definable Classes.
The Classes feature has proved tremendously popular as you'll see if you look at the number of recent threads where people are sharing their newly created Classes.
I'd say buy the 2 month licence if you feel that is all you need, but don't be surprised if you find yourself tempted to pay for an update after the 2 month period if the update contains some 'too good to be without' features.
Martin.