Hi Dan,
You should be able to do a green screen effect exactly the same in PD 11 as in PD 12 (I take it you just viewed the pointy hand tutorial by Adrian.)
PD 11 is still a very capable and powerful editor. I only upgraded because it has extra features and tweaks such as right click the transitions in the timeline and change the duration instead of having to manually go to the Preferences setting every time to do so. Some very subtle and some very major ones that caught my interest.
Since you are a newer user, I wouldn't sweat what the differences are. Just get comfortable with PD 11 and when your knowledge grows and you need more features then you have the option to upgrade to PD 12 and beyond.
.. and yes all NLEs and the different versions have their issues it's a given.
Rob
PD 14 Ultimate Suite / Win10 Pro x64
1. Gigabyte Brix PRO / i7-4770R Intel Iris Pro 5200 / 16 GB / 1 TB SSD
2. Lenovo X230T / 8GB / Intel HD4000 + ViDock 4 Plus & ASUS Nvidia 660 Ti / Link: https://www.youtube.com/watch?v=ZIZw3GPwKMo&feature=youtu.be