I have both Quickplan version 3, and Proplan (can't remember which version) on my computer. I bought Quickplan first. In fact I still prefer Quickplan and rarely use Proplan.
Quickplan 4 is nearly twice as expensive as Quickplan 3 was but I expect it is still excellent value for money.
If you want all the features of Proplan then it might be worth paying the extra for it, but like I say, I've gone back to using Quickplan.
At £17 its difficult to go wrong!