Need Help With a Stereo Antenna

Been watching some of the comments here so far. First let me say your 37 coupe is awesome looking. The color combo's are great together.
Im not sure what the shark fin antenna is. What I was looking at is a hidden antenna as well, Here's a link to one that I was looking at.
https://www.summitracing.com/parts/res-hpa1/reviews/
There are ones that are more expensive but from reading reviews a lot seems to depend on the unit you are going to be using. Im only concerned with the FM reception and it sounds as though these will work better on FM than on AM. Let me know how you make out once you decide what to use. I have at least a year before I will even be close to having my car on the road.
One last thing, I use XM/Sirius every day. I lose reception when I get into wooded areas, High banks on the side and underpasses. My XM radio I can pull out and put into my vette convertable, or my lexus. I connect it thru a cable to the sterio in either one and just sit it on my top dash. I find reception changes with the direction Im heading. If I am traveling in the direction away from a satellite and the roof blocks a direct path to the radio inside the car I lose reception. Now the radio I use has its own antenna built into it so I dont always have to have the XM antenna hooked up but Its not near as efficient with the auxillary antenna.
Keep your progress updated.
Best of Luck
Rod