So I have both windshields. And each have some pros and cons. I am going to try and explain all the advantages and disadvantages. I am 5'9 and I ride a 2009 road glide with a 103 stage II with Rinehart true duals. I wear glasses and live in a colder climate. A stock radio with Infinity Kapa speakers. (this will make more sense later)
I started on my glide with the 8" light smoke and bought a 12" dark smoke after reading some comments. I went back to the 8" and I will explain why. Each one works differently depending on riding conditions, and environment.
The 8" in my opinion looks better. The advantages for me are wind flow. Wait what? Yep, more wind on me helps. So I ride with a full face HJC helmet. The 8" has the air hit me right around my forehead. This helps keep the air flowing into the helmet and helps to keep from fogging, especially on colder days in Washington state. The 12" causes me to ride with the shield cracked open and I get a "shake" on my head. But because of the wind, I can only hear my radio up to about 60 mph clearly with the 8" version. After that, I really have to pay attention to the songs. I can only go up to about half way on the radio until it gets distorted.
The 12" has the air go over my head and around my shoulders. That being said, I can hear my radio pretty good up till about 70-75 mph. This is also better for a two up situation, as it is easier to hear my girlfriend on the back with the Scala rider set up.
In the summer, I really see no advantage to either other than the radio and communications. The 12" would work better than the 8" version if you need to hear things. Sure I can upgrade my radio and such. But I would rather spend my money on ammo or something .
These are just the observations I have seen with each shield. If you can afford both, great, if not, figure out what you need more. Both are far superior to the stock version. I think the Klock works look the best of all aftermarket shields. Some people will say get this brand or that brand, I am just trying to help people who are interested in the Klock works version.
Hope this helps. Have a great gliding day.