I sell industrial batteries and AGM deep cycle batteries we put in the Taylor Dunn electric vehicles I also sell. I would definitely stick with an AGM battery. The Harley batteries are AGM type and are obviously made by someone else.
But, the price is about normal $80-$90. I don't think I could get an AGM motorcycle battery much cheaper than $50 wholesale. So, for piece of mind, you should probably stick with the Harley battery. They seem to have a good track record from my research. I think Deka makes the batteries for Harley. Deka is the leading manufacture in batteries in the world and we sell a lot of Deka industrial batteries. I will probably get a Deka AGM wholesale when I need to replace my Harley AGM.