I have an A1-3.
The comb is pretty high. It has a notch cut out for the bolt.
I had an HTG before and found the comb to low. I liked the traditional grip, so chose the A1-3 to replace it. I've been happy. It's a pretty light and slim stock for the A series. I have no experience with Manners, but I haven't thought of switching my stock since I received the A1-3.
From looking at pictures, the biggest difference is going to be in the forends. The Manners is a wide beaver tail- Like the HSP stock on the 5R. Personally, I didn't like that stock. The A1-3 has a square forend. I like how it rides bags and the PRS cradle.