I have so far used Sibelius 3, Finale Notepad, Noteworthy Composer and the latest one being Overtue LE, because I myself purchased GPO a while ago.
Frankly, I think it has the features, but compared to the other ones I have used, Overture has an ugly interface with ugly shortcut keys - which is a must to me in a notation program.
Infact I am now mixed up in all these programs and there shortcuts! But I very much prefer Noteworthy, it is Perfect for notation by Computer Keyboard, and easy to set-up with GPO.
Only thing that frustrates me is the lack of N-plet feature in it, only Triplets are allowed, nothing more :/
By all means though, if you never used a notation program before, then Overture will probably be endurable, because you won't be used to anything easier, or possibly better by comparison. I really need to get used to it myself, Finale and Sibelius are Demo's on my computer, and you don't have all the features in Noteworthy. Overture does... but I love Noteworthy too much!
Anyway, that's all my opinion...
Topic: GPO question